POLICING FORENSIC EVIDENCE

AMERICAN JOURNAL
of LAW and EQUALITY

Brandon L. Garrett*

INTRODUCTION

If there had been no video of Derek Chauvin killing George Floyd on May 25, 2020, the
legal and public response might have been quite diﬀerent. Before a series of videos cap-
tured by witnesses and security cameras surfaced, the Minneapolis Police Department is-
sued a statement: “After Floyd got out of his car, he physically resisted oﬃcers. Oﬃcers
were able to get the suspect into handcuﬀs and noted he appeared to be suﬀering medical
distress.”1 The Chief Medical Examiner for the county did determine that Floyd’s death
was a homicide but also speculated that Floyd suﬀered from “signiﬁcant conditions,” such
as drug use and a heart condition, that may have increased his likelihood of death.2
At Chauvin’s trial, the medical examiner testiﬁed, “In my opinion, the law enforcement
subdual, restraint, and the neck compression was just more than Mr. Floyd could take
by virtue of those heart conditions.”3 Attorneys for Floyd’s family commissioned an

*L. Neil Williams, Jr. Professor of Law, Duke University School of Law, and Director, Wilson Center for Science and
Justice.

See Investigative Update on Critical Incident, INSIDE MINNEAPOLIS POLICE DEP’T (May 25, 2020), https://web.archive
.org/web/20200526183652/ https://www.insidempd.com/2020/05/26/man-dies-after-medical-incident-during
-police-interaction/; see also Philip Bump, How the First Statement from Minneapolis Police Made George Floyd’s
Murder Seem Like George Floyd’s Fault, WASH. POST (Apr. 20, 2021), https://www.washingtonpost.com/politics
/2021/04/20/how-ﬁrst-statement-minneapolis-police-made-george-ﬂoyds-murder-seem-like-george-ﬂoyds-fault/.
See HENNEPIN COUNTY MEDICAL EXAMINER’S OFFICE AUTOPSY REPORT ( June 1, 2020), https://www.hennepin.us/-
/media/hennepinus/residents/public-safety/medical-examiner/ﬂoyd-autopsy-6-3-20.pdf (citing, as the “case
title,” “cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression”); see
also Bill Chappell & Laurel Wamsley, Video: Medical Examiner Says Police Restraint ‘Just More Than Mr.
Floyd Could Take,’ NPR (Apr. 9, 2021, 5:55 PM ET), https://www.npr.org/sections/trial-over-killing-of-george
-ﬂoyd/2021/04/09/985722945/live-video-medical-examiner-to-testify-about-george-ﬂoyds-death.
Chappell & Wamsley, supra note 2.

© 2022 Brandon L. Garrett. Published under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0
International license (CC BY-NC-ND).
https://doi.org/10.1162/ajle_a_00042

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independent autopsy that found that there were no such contributing factors.4 More spe-
ciﬁcally, they found that the cause of death was not a heart attack but rather “mechanical
asphyxia”—meaning the ﬂow of oxygen was cut oﬀ so Floyd, as he told the oﬃcers, simply
could not breathe.5 As Martin Tobin testiﬁed at the criminal trial, given the force placed
on Floyd’s neck, “[a] healthy person subjected to what Mr. Floyd was subjected to would
have died.”6

It was not an aberration that the medical examiner’s determinations regarding cause of
death were hotly disputed. There is a long, troubling history of prosecution, in media re-
leases, labeling people killed by police as criminals or drug users or persons with preex-
isting medical conditions.7 Forensic evidence, in which medical examiners or coroners set
out conclusions in death certiﬁcates, has played a troubling role in providing faulty sup-
port for such claims.8 All too often, questionable ﬁndings have been shared with the public
and our courts, including by omitting entirely the role of police in cases of police killings.9
The coroner and medical examination ﬁeld is rife with poor methods. A landmark 2009
National Academy of Sciences report (“NAS Report”) called death investigations in the
United States “fragmented” as a system that is “deﬁcient” in its practices and called for
the replacement of local coroners’ oﬃces with a medical examiner system.10

The Floyd case is just one high-proﬁle example of a larger problem: police evidence col-
lection, including when it is conducted with outside experts and crime labs, lacks adequate
scientiﬁc safeguards and as a result is prone to bias and error.11 A central function of policing
is to gather evidence during criminal investigations. Law enforcement receives a great deal of
deference when it carries out those investigative functions. While detailed constitutional
criminal procedure rules regulate traditional policing functions, such as searches and seizures,
there is very little regulation of forensic evidence of any kind, much less regulation informed
by community priorities, research, or policy.12 To be sure, a growing number of police

5
6
7

9
10

See Bill Chappell & Vanessa Romo, Chauvin Trial: Expert Says George Floyd Died from a Lack of Oxygen, Not
Fentanyl, NPR (Apr. 8, 2021, 6:18 PM ET), https://www.npr.org/sections/trial-over-killing-of-george-ﬂoyd/2021
/04/08/985347984/chauvin-trial-medical-expert-says-george-ﬂoyd-died-from-a-lack-of-oxygen.
Id.
Id.
See Sam Levin, Killed by Police, Then Viliﬁed: How America’s Prosecutors Blame Victims, GUARDIAN, Mar. 21, 2019;
see also Samantha Michaels, Why Coroners Often Blame Police Killings on a Made-Up Medical Condition, MOTHER
JONES, Oct. 14, 2020 (discussing attributions of deaths to drug overdose or excited delirium).
See Tim Arango & Shaila Dewan, More Than Half of Police Killings Are Mislabeled, New Study Says, N.Y. TIMES
(Sept. 30, 2021), https://www.nytimes.com/2021/09/30/us/police-killings-undercounted-study.html.
Id.
See COMM. ON IDENTIFYING THE NEEDS OF THE FORENSIC SCIS. CMTY. & NAT’L RSCH. COUNCIL, STRENGTHENING FORENSIC
SCIENCE IN THE UNITED STATES: A PATH FORWARD 29 (2009) [hereinafter NAS REPORT].
For a much more comprehensive account, see BRANDON L. GARRETT, AUTOPSY OF A CRIME LAB: EXPOSING THE FLAWS
IN FORENSICS (2020).
Paul C. Giannelli, Wrongful Convictions and Forensic Science: The Need to Regulate Crime Labs, 86 N.C. L. REV.
163 (2007).

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POLICING FORENSIC EVIDENCE

policies and guidelines reﬂect the recent eﬀort to emphasize accurate and impartial evidence
collection. The International Association of Chiefs of Police has taken an active role in
promoting the consideration of ways to improve the “accuracy and thoroughness” of police
investigations.13 Far more is needed to ensure such accuracy and thoroughness.

A second example of forensics gone wrong illustrates the problem, not in the medical
examiner setting but in the crime laboratory setting. The Department of Forensic Science
(DFS) in Washington, D.C., was supposed to be a model lab that would change lab work
on crime scene evidence for the better. The D.C. government passed the Department of
Forensic Sciences Act of 2011 to make the lab more independent of police and require it to
be accredited.14 It paid tens of millions of dollars for a large new facility.15 Unfortunately,
while accredited crime labs may have more in the way of quality control than a typical
policing agency, they do not have the quality controls present in a scientiﬁc or clinical lab.
In a murder trial, Judge Todd Edelman ruled in August 2019 that after hearing from
several experts at an extensive hearing, he was concerned that published studies had not
been able to show that DFS examiners could reliably make a “source attribution.”16 The
judge held that the most an expert could say for the government was that “the recovered
ﬁrearm [could not] be excluded as the source of the cartridge casing found on the scene of
the alleged shooting.”17 A new case involving ﬁrearms evidence analyzed in 2017 and
charges against two men for two killings was in front of Judge Edelman.18 The ﬁrearms
group at the lab had reported that the same weapon ﬁred the cartridges in the two shoot-
ings.19 Perhaps because Judge Edelman had been skeptical in the past, the prosecutors
wanted to make sure; they took an unusual step and asked an independent examiner to
take a look at the evidence.20 That examiner was sure that it was clear that two diﬀerent

INTERNATIONAL ASS’N OF CHIEFS OF POLICE, NATIONAL SUMMIT ON WRONGFUL CONVICTIONS: BUILDING A SYSTEMIC
APPROACH TO PREVENT WRONGFUL CONVICTIONS 10 (2013).
See D.C. CODE § 5–1501.02 ( West 2022) (“There is established as a subordinate agency in the executive branch of
the government of the District of Columbia, the Department of Forensic Sciences.”).
Editorial Board, D.C.’s New Crime Lab Goes Under the Microscope, WASH. POST (Mar. 11, 2015), https://www
.washingtonpost.com/opinions/dcs-new-crime-lab-goes-under-the-microscope/2015/03/11/fe48dfd2-c442-11e4
-ad5c-3b8ce89f1b89_story.html.

16 Memorandum Opinion at *1, Tibbs v. United States, No. 2016 CF1 19431 (D.C. Super. Ct. Sept. 5, 2019), https://
context-cdn.washingtonpost.com/notes/prod/default/documents/cc85da89-f6a1-4172-bf1c-b6b759669687/note
/2faab6e6-85da-4abe-a669-b9f48db2498e.pdf (“According to the government’s proﬀer, this analysis permitted the
examiner to identify the recovered ﬁrearm as the source of the cartridge casing collected from the scene.”).
Id. (“[T]he government’s expert witness must limit his testimony to a conclusion that, based on his examination
of the evidence and the consistency of the class characteristics and microscopic toolmarks, the ﬁrearm cannot be
excluded as the source of the casing.”).
Jack Moore, DC Judge Orders Forensic Lab to Turn Over Some Documents Sought by Prosecutors, WTOP NEWS
(Dec. 10, 2020, 2:34 PM), https://wtop.com/dc/2020/11/dc-judge-orders-forensic-lab-to-turn-over-some
-documents-sought-by-prosecutors/.
Id.
Id.

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ﬁrearms were involved.21 The lab deﬁantly insisted the outside examiner was wrong and
that in fact the examiner’s report was an “administrative error” and the evidence was now
deemed to be “inconclusive.”22

The lab went into damage control mode. The lab director called it a “darn good lab.”23
Management told the American National Standards Institute National Accreditation
Board, which accredited the lab, that it had made an “inconclusive” ﬁnding after initiating
a review of the incident. In April 2020, the lab’s accreditation was suspended.24 The lab
entirely stopped doing work as a result. Prosecutors opened a new probe into the ﬁrearms
unit and disagreed with the lab in eleven cases. A scathing audit report found that lab
managers sought to conceal the problem in the case before Judge Edelman and pressured
others to report that the ﬁnding was “inconclusive.”25 One examiner recalled how he tried
to “push back as long as he could” and wished he had resigned in protest.26 The auditors
concluded that this illustrated “very serious” problems with management that indicated
lack of adherence to “core principles of integrity” and ethics. The lab director resigned.
A letter alleged “potential concealment” of errors in the ﬁngerprint unit as well.27 In
September 2021, the lab disbanded the ﬁrearms unit. A criminal investigation of the
lab is pending, and the lab remains closed.28

As these high-proﬁle examples both show, forensic evidence has, to varying degrees,
left the police station for the laboratory in a manner that represents a highly incomplete
and much-needed transition to sound science. In recent years, the scientiﬁc community
has called for forensic work to be independent of police so it can adhere to sound scientiﬁc
standards. The central recommendation of the NAS Report, which brought together lead-
ing scientists to consider the path forward for forensic science, centered on independence
and scientiﬁc methods.29 At best, some crime labs have obtained ﬁnancial but not

21
22
23

26
27

Id.
Id.
Jack Moore & Megan Cloherty, ‘You Can Trust This Laboratory’: DC Crime Lab Director Responds to Scrutiny of
Firearms Unit, WTOP NEWS (Dec. 2, 2020, 4:24 AM), https://wtop.com/dc/2020/12/you-can-trust-this-laboratory
-dc-crime-lab-director-responds-to-scrutiny-of-ﬁrearms-unit/.
Keith L. Alexander, National Forensic Science Board Suspends D.C. Crime Lab’s Accreditation, Halting Analysis of
Evidence, City Says, WASH. POST (Apr. 3, 2021), https://www.washingtonpost.com/local/public-safety/dc-lab
-forensic-evidence-accreditation/2021/04/03/723c4832-94aa-11eb-a74e-1f4cf89fd948_story.html.
Praecipe, U.S. v. McLeod, No. 2017 CF1 9869 (D.C. Super. Ct. Mar. 22, 2021), https://wtop.com/wp-content
/uploads/2021/03/rondell_mcleod_dfs_court_ﬁling_march_22.pdf.
Id.
Paul Wagner, DC Crime Lab Under Investigation After Allegations of Wrongdoing, NBC NEWS (Apr. 8, 2021,
8:40 PM), https://www.nbcwashington.com/news/ local/dc-crime-lab-under-investigation-after-allegations-of
-wrongdoing/2634489/.
Jack Moore, DC Abruptly Disbands Crime Lab’s Firearms Unit, WTOP NEWS (Sept. 16, 2021, 4:00 PM), https://
wtop.com/dc/2021/09/dc-abruptly-disbands-crime-labs-ﬁrearms-unit/.
See NAS REPORT, supra note 10.

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structural independence from law enforcement with the accountability and accuracy that
should accompany an embrace of scientiﬁc methods.

Many are asking new questions about how to deﬁne public safety.30 Even in the area of
forensic evidence, where there is a greater expectation that science will be used in service
of public safety, questions about the police’s role in collecting and testing evidence have
remained unasked. Far too often, untrained police, rather than trained scientists, collect
and potentially alter or contaminate evidence at crime scenes.31 Further, we allow law en-
forcement oversight of most crime labs, or we allow law enforcement and prosecutors to
direct and inﬂuence their work, practices that would never be tolerated in a scientiﬁc ex-
periment, much less a scientiﬁc lab.32 As police deploy new technologies, these questions
will hopefully continue to be asked, but little scrutiny has resulted when old technologies,
like pathology examinations or ﬁngerprint comparisons, have been used. One reason these
practices remain under-examined is that neither courts nor the public can readily access
what procedures crime labs employ or what results they obtain.

However, the movement to bring scientiﬁc standards to forensics, which is increasingly
embraced by the forensic community and legal actors, has the potential to address these
long-standing needs. As I discuss in this essay, that movement also has promise for policing
more generally. We should be using quality controls to regulate crime labs, and policing
more broadly, to evaluate the fairness and public safety of outcomes. The focus here is
on three speciﬁc core principles that can improve the role of forensic evidence in policing:
(1) independence, (2) accuracy, and (3) oversight.

INDEPENDENCE AND FORENSIC EVIDENCE

The NAS Report warned that a “lack of independence” of crime labs from law enforce-
ment can damage the objectivity of forensic science and harm criminal justice.33

Daniel S. Nagin, Cost-Beneﬁt Analysis of Crime Prevention Policies, 14 CRIMINOLOGY & PUB. POL’Y 583, 585 (2015);
Barry Friedman & Elizabeth Jansky, Policing’s Information Problem (2019), https://papers.ssrn.com/sol3/papers
.cfm?abstract_id=3452242; Barry Friedman, We Spend $100 Billion on Policing. We Have No Idea What
Works., WASH. POST (Mar. 10, 2017), https://www.washingtonpost.com/posteverything/wp/2017/03/10/we
-spend-100-billion-on-policing-we-have-no-idea-what-works/.
For an in-depth analysis of this problem, see Jennifer E. Laurin, Remapping the Path Forward: Toward A Systemic
View of Forensic Science Reform and Oversight, 91 TEX. L. REV. 1051, 1081 (2013); see also FRANK HORVATH ET AL., A
NATIONAL SURVEY OF POLICE POLICIES AND PRACTICES REGARDING THE CRIMINAL INVESTIGATION PROCESS: TWENTY-FIVE
YEARS AFTER RAND 76 (2001), https://www.ncjrs.gov/pdﬃles1/nij/grants/202902.pdf (“[I]n most agencies evidence-
related duties are not assigned predominantly to any one type of individual or position. Rather, they are more
likely to be shared among patrol oﬃcers . . . investigators . . . and evidence technicians . . . .”).
For the authoritative account, see SANDRA GUERRA THOMPSON, COPS IN LAB COATS: CURBING WRONGFUL CONVICTIONS
THROUGH INDEPENDENT FORENSIC LABORATORIES 181–83 (2015).
See NAS REPORT, supra note 10.

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Traditionally, forensic evidence has largely been a law enforcement function, not a scien-
tiﬁc function, in the United States. Early crime labs were small and operated by police
departments, following the early example of the Federal Bureau of Investigation (FBI)
lab.34 By the 1960s, every state had crime labs run by law enforcement.35 Today, there
are over four hundred publicly funded crime labs with over 14,300 lab employees.36 Very
few labs in the United States are independent from law enforcement.

Nor is the work done by professionals necessarily independent of law enforcement.
This problem begins at the crime scene. Such work may be conducted by a variety of pro-
fessionals and roles, including oﬃcers working for police departments but also crime-lab
analysts, technicians, and others.37 Evidence collection may be conducted by law enforce-
ment. Law enforcement priorities and resources may aﬀect the initial decision whether to
test evidence. Recent inquiries and audits have resulted when labs have failed to test fo-
rensic evidence, particularly regarding untested rape kits. One study found that forty per-
cent of unanalyzed rape and homicide cases were estimated to have testable DNA.38 In Los
Angeles County, following a 2009 Human Rights Watch report and public protests, police
and sheriﬀs began to work to address years of backlogs.39 In response to the serious prob-
lem of non-testing, and with federal grant support,40 twenty-six states have enacted stat-
utes requiring inventories of untested sexual assault evidence.41

Police begin the process of examining forensic evidence when they collect evidence at
the crime scene. Police often do not have policies regarding sound and scientiﬁc collection
of crime scene evidence, which then aﬀects the work done by a lab.42 There has been a
recent focus on developing policies and procedures for crime scene evidence collection,

Paul Giannelli, Forensic Science: Why No Research?, 38 FORDHAM URBAN L.J. 503 (2010).
See John I. Thornton, Criminalistics: Past, Present and Future, 11 LEX ET SCIENTIA 23 (1975).

34
35
36 MATTHEW R. DUROSE ET AL., BUREAU OF JUST. STAT., U.S. DEP’T OF JUST., CENSUS OF PUBLICLY FUNDED FORENSIC CRIME

LABORATORIES, 2009, at 1 (2012), https://bjs.ojp.gov/content/pub/pdf/cpﬀcl09.pdf.
See JOSEPH PETERSON & IRA SOMMERS, THE ROLE AND IMPACT OF FORENSIC EVIDENCE IN THE CRIMINAL JUSTICE PROCESS 22
(2010).
KEVIN J. STROM ET AL., 2007 SURVEY OF LAW ENFORCEMENT EVIDENCE PROCESSING: FINAL REPORT 4–5 (2009).
HUM. RTS. WATCH, TESTING JUSTICE: THE RAPE KIT BACKLOG IN LOS ANGELES CITY AND COUNTY (2009), https://www
.hrw.org/sites/default/ﬁles/reports/rapekit0309web.pdf.
The SAFER Act of 2013, Pub. L. No. 113-4, § 1002, 127 Stat. 54, 127–131 (authorizing use of grants under the
Debbie Smith DNA Backlog Grant Program (34 U.S.C. § 40701) to conduct audits of sexual assault evidence and
requiring the Attorney General to publish information from audits online); see also Sexual Assault Kit Initiative
(SAKI), BUREAU OF JUST. ASSISTANCE, DEP’T OF JUST. PROGRAM, https://www.bja.gov/ProgramDetails.aspx?Program
_ID=117 (last visited Dec. 2018).
U.S. GOV’T ACCOUNTABILITY OFF., GAO-19-216, DNA EVIDENCE: DOJ SHOULD IMPROVE PERFORMANCE MEASUREMENT
AND PROPERLY DESIGN CONTROLS FOR NATIONWIDE GRANT PROGRAM 16 (2019), https://www.gao.gov/assets/700
/697768.pdf.
HORVATH ET AL., supra note 31; Laurin, supra note 31, at 1081.

38
39

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including to promote the use of forensic professionals at the crime scene.43 Not only do
police often lack the resources or training to adequately collect evidence at the crime scene,
but they often fail to collect evidence that could be highly probative.44 Police may also
preemptively test evidence themselves using inaccurate ﬁeld methods. For example, com-
mercial drug-testing kits are often not carefully validated; the few studies conducted on
this issue have shown that these kits can have high error rates. The ﬁeld tests are supposed
to be followed up with a more rigorous lab test, but in the meantime, a person may be
arrested and face great pressure to plead guilty. In Harris County, Texas, an audit by the
District Attorney’s Oﬃce Conviction Integrity Unit uncovered hundreds of such cases.
The Texas Forensic Science Commission later found these tests too unreliable for use
and the convictions were subsequently reversed.45 In 2017, Houston police ceased use
of ﬁeld drug tests, but they remain widely used in other jurisdictions.

In other areas, bias in police evidence collection can be of constitutional concern. For
example, the U.S. Supreme Court has found highly suggestive and unreliable practices in
the area of eyewitness identiﬁcations that may violate the Due Process Clause. The Court’s
ruling in Manson v. Brathwaite set out a due process test using a series of so-called reli-
ability factors to assess eyewitness identiﬁcations in which police used suggestive
procedures.46

No such inquiry exists for forensic evidence. A large body of research has now docu-
mented how cognitive biases can aﬀect forensic work. Psychological research has shown
how where forensic techniques involve some degree of judgment and interpretation, ex-
perts are vulnerable to cognitive bias.47 In the laboratory, testing is rarely blind, and a
range of communications with law enforcement can bias the test results. Traditionally,
beginning with the submission of evidence, the forensic analysts communicate with law
enforcement about evidence in the case and hear task-irrelevant and biasing information.

44
45

See, e.g., NAT’L FORENSIC SCI. TECH. CTR. (NFSTC), CRIME SCENE INVESTIGATION: A GUIDE FOR LAW ENFORCEMENT
(2014), https://shop.nfstc.org/crime-scene-investigation-guide/; SUE BALLOU ET AL., THE BIOLOGICAL EVIDENCE
PRESERVATION HANDBOOK: BEST PRACTICES FOR EVIDENCE HANDLERS (2013), https://www.nist.gov/system/ﬁles
/documents/forensics/NIST-IR-7928.pdf.
See PETERSON & SOMMERS, supra note 37, at 22.
Ryan Gabrielson, Texas Panel on Wrongful Convictions Calls for Ending Use of Unveriﬁed Drug Field Tests,
PROPUBLICA ( Jan. 18, 2017, 12:48 PM EST ), https://www.propublica.org/article/texas-panel-wrongful
-convictions-calls-end-use-unveriﬁed-drug-ﬁeld-tests.

46 Manson v. Brathwaite, 432 U.S. 98, 114 (1977).
47

EXEC. OFF. OF THE PRESIDENT, PRESIDENT’S COUNCIL OF ADVISORS ON SCI. & TECH. (PCAST), FORENSIC SCIENCE IN
CRIMINAL COURTS: ENSURING SCIENTIFIC VALIDITY OF FEATURE-COMPARISON METHODS 8 (2016), https://
obamawhitehouse.archives.gov/sites/default/ﬁles/microsites/ostp/PCAST/pcast_forensic_science_report_ﬁnal.pdf
[hereinafter PCAST REP.] (“The ﬁndings of forensic science experts are vulnerable to cognitive and contextual
bias.”).

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In one of the most famous studies in all of forensics, ﬁve highly experienced ﬁnger-
print examiners reviewed a set of prints in the course of their ordinary work.48 The ex-
aminers did not know that Professor Itiel Dror and colleagues had given these examiners
prints that each of the ﬁve had looked at years before in a real-life case and had found then
to be from the same source.49 Other experts had separately looked at those prints and
agreed that they were from the same source. Dror and colleagues informed the ﬁve exam-
iners that the prints were from the infamous Madrid bombing case, in which three senior
FBI examiners mistakenly implicated an innocent Portland, Oregon, lawyer.50 After hav-
ing been told that these prints were from that case, in which such a high-proﬁle error had
been made, four of the ﬁve reached a diﬀerent conclusion: one persisted in reporting that
the prints came from the same source, three now concluded these were “deﬁnite non-
match” prints, and the fourth called the evidence “inconclusive.”51

Addressing cognitive bias is only now becoming a central part of quality control at
crime laboratories. Adoption of procedural protections can reduce such bias. For example,
a linear sequential approach has been developed for comparative pattern disciplines. The
2016 President’s Council of Advisors on Science and Technology (PCAST) Report recom-
mends that approach for ﬁngerprint comparisons: an examiner “should be required to
complete and document their analysis of a latent ﬁngerprint before looking at any known
ﬁngerprint” to prevent circular reasoning where looking back and forth between prints
encourages an expert to disregard diﬀerences.52 A second protection is to ensure that po-
tentially biasing task-irrelevant information is not passed on to lab analysts.53 The PCAST
Report also recommended that a ﬁngerprint examiner “should separately document any
additional data used during their comparison and evaluation.”54 Information is task-
irrelevant if it is not necessary for drawing conclusions about the propositions in question,
using the method in question. Separation of roles in a laboratory can help keep task-
irrelevant information from biasing analysts.55 Such procedures are much needed to deﬁne

49
50
51
52

54
55

I. E. Dror et al., Contextual Information Renders Experts Vulnerable to Making Erroneous Identiﬁcations, 156
FORENSIC SCI. INT’L. 74, 77 (2006). (“Our study shows that it is possible to alter identiﬁcation decisions on the
same ﬁngerprint, solely by presenting it in a diﬀerent context.”).
Id.
Id.
Id.
See PCAST REP., supra note 47, at 10; see also Dan E. Krane et al., Sequential Unmasking: A Means of Minimizing
Observer Eﬀects in Forensic DNA Interpretation, 53 J. FORENSIC SCIS. 1006–07 (2008); Itiel E. Dror et al., Context
Management Toolbox: A Linear Sequential Unmasking (LSU) Approach for Minimizing Cognitive Bias in Forensic
Decision Making, 60 J. FORENSIC SCIS. 1111 (2015).
See NAT’L COMM’N ON FORENSIC SCI., ENSURING THAT FORENSIC ANALYSIS IS BASED UPON TASK-RELEVANT INFORMATION 2
(2015), https://www.justice.gov/archives/ncfs/page/ﬁle/641676/download.
See PCAST REP., supra note 47, at 10.
See Itiel E. Dror, A Hierarchy of Expert Performance, 5 J. APPLIED RSCH. IN MEMORY AND COGNITION 121–27 (2016).

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the relationships between law enforcement and crime labs, and they should be a hallmark
of functionally independent and sound science.56 Those reforms are only slowly being
implemented, however.

II. ACCURACY

A wide range of scientiﬁc and legal actors, including scientists, forensic practitioners, law-
makers, lawyers, and judges, have called for greater reliability in forensics. The National
Academy of Sciences Report in 2009 emphasized that “some forensic science disciplines are
supported by little rigorous systematic research to validate the discipline’s basic premises
and techniques.” Slowly, as such research has begun to be conducted, we have learned just
how often forensic methods go wrong.57

The legal response has been relatively piecemeal. Many states now follow standards
based on the U.S. Supreme Court’s ruling in Daubert v. Merrell Dow Pharmaceuticals58
and its progeny, which task judges with greater gatekeeping responsibilities to assess
the reliability of scientiﬁc evidence. Those rules are widely understood to be ineﬀectively
used in criminal cases. Leading reports, such as the inﬂuential 2009 National Academy of
Sciences Report, have noted that lawyers and judges have not taken an active or eﬀective
role in reviewing the reliability of forensic evidence in criminal cases.59 Constitutional
criminal procedure bars the failure to disclose exculpatory evidence and the outright fab-
rication of evidence by law enforcement. The U.S. Supreme Court has long held that fab-
ricating evidence or knowingly using perjured testimony violates the Due Process
Clause.60 In addition, oﬃcers and prosecutors must supply “any favorable evidence known
to others acting on the government’s behalf in the case, including the police.”61 No con-
stitutional rules regulate the reliability of forensic evidence, apart from those elemental
disclosure and non-fabrication rules.

For decades, forensic analysts of diﬀerent types testiﬁed they were one hundred per-
cent certain of their conclusions.62 As federal judge Harry T. Edwards put it, “The courts
had been misled for a long time because we had been told, my colleagues and I, by some

57
58
59

60
61
62

For an example of a simple checklist that can assist with such work, see Adele Quigley-McBride et al., A Practical
Tool for Information Management in Forensic Decisions: Using Linear Sequential Unmasking-Expanded (LSU-E)
in Casework, 4 FORENSIC SCI. INT’L: SYNERGY 100216 (2022).
See PCAST REP., supra note 47, at 56 (discussing black box studies conducted for certain disciplines).
Daubert v. Merrell Dow Pharms., 509 U.S. 579 (1993).
See NAS Report, supra note 10; Peter J. Neufeld, The (Near) Irrelevance of Daubert to Criminal Justice and Some
Suggestions for Reform, 95 AM. J. PUB. HEALTH S107, S110 (2005).
Napue v. Illinois, 360 U.S. 264 (1959); Mooney v. Holohan, 294 U.S. 103 (1935).
Kyles v. Whitley, 514 U.S. 419, 437 (1995).
See Alex Biedermann et al., After Uniqueness: The Evolution of Forensic-Science Opinions, JUDICATURE, Spring 2018,
https://judicature.duke.edu/articles/after-uniqueness-the-evolution-of-forensic-science-opinions/.

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experts from the FBI that ﬁngerprint comparisons involved essentially a zero error rate,
without our ever understanding that’s completely inaccurate.”63 Yet, no one had carefully
tested the basic assumptions that experts have relied upon for decades. More recently, the
NAS and PCAST Reports highlighted the need for scientiﬁc testing of the reliability of
core forensic disciplines. The PCAST Report detailed how for a more objective method,
like a drug test, you can evaluate each step in the process by seeing whether it produces
accurate results.64 However, for subjective techniques like pattern evidence comparisons,
there are no clearly deﬁned steps. The person is the process: an examiner’s mind is a
“black box” that reaches judgments based on training and experience.65 To test such a
“black box” examiner, one can give tests with samples of realistic diﬃculty and with the
correct answer known in advance.66 In forensics, that type of proﬁciency testing is not
routine in labs, as part of quality control or performance testing of examiners, except using
very elementary tests that are not designed to be rigorous.67 Entire ﬁelds have lacked such
testing to establish reliability. And, as the PCAST Report underscored, “without appropri-
ate estimates of accuracy, an examiner’s statement that two samples are similar—or even
indistinguishable—is scientiﬁcally meaningless: it has no probative value, and considerable
potential for prejudicial impact.”68 For example, the PCAST Report described that, while
several early studies had been conducted and documented high error rates, just two prop-
erly designed studies of the accuracy of latent ﬁngerprint analysis had been conducted to
date.69 That alone is deeply disturbing, given the prominence of ﬁngerprint evidence in
criminal investigations and prosecutions over the past hundred years. It was generous for
the report to say that just two studies would be enough to permit a technique to be used in
criminal cases. Indeed, the people participating in the studies knew that they were being
tested and that it was important for the ﬁeld. They were likely very cautious in their work,
and they could drop out of the study, including if they found a question challenging and
they feared making an error. In the larger of the two studies—the only one published—a
huge group, eighty-ﬁve percent of the examiners, made at least one false negative error.70

64
65

66
67
68
69
70

See Lowell Bergman, The Real CSI, FRONTLINE, https://www.pbs.org/wgbh/frontline/ﬁlm/real-csi/transcript/ (last
visited June 23, 2022).
See PCAST REP., supra note 47, at 56.
Id. at 5–6 (stating that for subjective feature comparison methods, because the individual steps are not objectively
speciﬁed, the method must be evaluated as if it were a “black box” in the examiner’s head).
Id. at 6.
See Brandon L. Garrett & Gregory Mitchell, The Proﬁciency of Experts, 166 U. PA. L. REV. 901 (2018).
PCAST REP., supra note 47, at 6.
See id. at 98.
See Bradford T. Ulery et al., Accuracy and Reliability of Forensic Latent Fingerprint Decisions, 108 PROC. NAT’L
ACAD. SCIS. 7733 (2011) (“Eighty-ﬁve percent of examiners made at least one false negative error for an overall
false negative rate of 7.5%.”).

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POLICING FORENSIC EVIDENCE

These ﬁndings provided another overdue wake-up call. It would shock jurors to hear of
such error rates, and it would aﬀect their convictions.71

The 2009 National Academy of Sciences Report similarly concluded that there needs
to be more research “to conﬁrm the fundamental basis for the science of bite mark compar-
ison.”72 It said that the uniqueness of human dentition has “not been scientiﬁcally estab-
lished.”73 The scientists who wrote the PCAST Report concluded that since no valid studies
of error rates had been done, the analysis lacked validity and should not be used.74 What
we do know about reliability is disturbing, as the PCAST Report detailed.75 None of these
troubling ﬁndings blunted the force of standard testimony on bite marks delivered in
court, nor did forensic dentists make a habit of describing these studies in reports or tes-
timony; indeed, courts continue to allow the evidence in criminal trials.76

Of particular importance to police investigations, in part because ﬁrearms violence is a
major problem in the United States, is that ﬁrearms comparisons are in great demand. To
complete such analysis, examiners seek to link crime scene evidence, such as spent shell
casings or bullets, with a ﬁrearm.77 The assumption is that manufacturing processes leave
markings on the barrel, breech face, and ﬁring pin. When the ﬁrearm discharges, those
components contact the ammunition and leave marks on it.78 Experts have assumed that
diﬀerent ﬁrearms should leave diﬀerent toolmarks on the ammunition such that the spent
ammunition can be deﬁnitively linked to a single ﬁrearm.79 By the late 1990s, experts pre-
mised testimony on a “theory of identiﬁcation” set out by a professional association, the
Association of Firearms and Tool Mark Examiners (AFTE), which instructs practitioners
to use the phrase “source identiﬁcation” to explain what they mean when they identify
“suﬃcient agreement” when examining ﬁrearms.80 The AFTE’s theory is circular: an iden-
tiﬁcation occurs when the expert ﬁnds suﬃcient evidence deﬁned as suﬃcient to ﬁnd an
identiﬁcation.81 In recent years, scientists have called into question the validity and

72
73
74

76
77
78
79
80
81

See Brandon L. Garrett et al., Error Rates, Likelihood Ratios, and Jury Evaluation of Forensic Evidence, 65 J.
FORENSIC SCIS. 1199 (2020).
See NAS Report, supra note 10.
Id.
See PCAST REP., supra note 47, at 87 (“PCAST ﬁnds that bitemark analysis does not meet the scientiﬁc standards
for foundational validity, and is far from meeting such standards. To the contrary, available scientiﬁc evidence
strongly suggests that examiners cannot consistently agree on whether an injury is a human bitemark and cannot
identify the source of bitemark with reasonable accuracy.”).
See PCAST REP., supra note 47, at 87 (“Among those studies that have been undertaken, the observed false
positive rates were so high that the method is clearly scientiﬁcally unreliable at present.”).
See GARRETT, AUTOPSY OF A CRIME LAB, supra note 11, at 127–29, 197.
See PCAST REP., supra note 47, at 104.
Id.
Id.
Id.
Id.

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reliability of such testimony. In a 2008 report on ballistics imaging, the National Academy
of Sciences (NAS) concluded that deﬁnitive associations like “source identiﬁcation” were
not supported.82 In its 2009 report, the NAS followed up and stated that categorical con-
clusions regarding ﬁrearms or toolmarks were not supported by research and that, instead,
more cautious claims should be made.83 The report stated that the “scientiﬁc knowledge
base for tool mark and ﬁrearms analysis is fairly limited.”84 The AFTE theory of identi-
ﬁcation “is inadequate and does not explain how an expert can reach a given level of con-
ﬁdence in a conclusion.”85

By 2016, only a single black box study on ﬁrearms comparisons had been done, and it
showed an error rate as high as 1 in 46.86 This single study is unpublished, and it raises
many of the same concerns as other studies in which participants were aware that their
assignment was a test and in which some could and did drop out after reviewing the ma-
terials.87 The rate of inconclusive errors was over thirty-three percent.88 To this day, ﬁre-
arms examiners use terms like “source identiﬁcation” in court—and avoid reporting what
is known about error rates. Some judges have begun to step in and require more cautious
wording for ﬁrearms conclusions.89 However, crime lab regulation is needed, as described
next, just as other scientiﬁc laboratories are regulated.

III. OVERSIGHT OF CRIME LABS

There are some ways in which crime labs can be a model for policing agencies. Forensic
evidence should bring with it better documentation, scientiﬁc methods, and quality con-
trols, which are broadly needed in the criminal system. Forensic examiners must follow lab
protocols to document their work; police detectives and patrol oﬃcers should be held to
higher standards regarding documentation of their investigative work. Forensic labs may
be accredited and are required to adopt certain quality control standards. In addition,

82
83
84
85
86

88
89

See NAT’L RSCH. COUNCIL, BALLISTIC IMAGING 3–4 (2008).
See NAS Report, supra note 10, at 154.
Id.
Id.
See PCAST REP., supra note 47, at 11 (“The scientiﬁc criteria for foundational validity require that there be more
than one such study, to demonstrate reproducibility, and that studies should ideally be published in the peer-
reviewed scientiﬁc literature. Accordingly, the current evidence still falls short of the scientiﬁc criteria for
foundational validity.”).
See DAVID P. BALDWIN ET AL., DEF. BIOMETRICS & FORENSICS OFF., ASSISTANT SEC’Y OF DEF., A STUDY OF FALSE-POSITIVE
AND FALSE-NEGATIVE ERROR RATES IN CARTRIDGE CASE COMPARISONS (Technical Report #IS-5207) 9 (2014),
https://afte.org/uploads/documents/swggun-false-postive-false-negative-usdoe.pdf.
See PCAST REP., supra note 47, at 110.
Regarding the eﬀectiveness of such measures, see Brandon L. Garrett et al., Mock Jurors’ Evaluation of Firearm
Examiner Testimony, 44 LAW & HUM. BEHAV. 412 (2020).

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forensic examiners are subjected to periodic proﬁciency testing, which, in theory, exam-
ines the quality of their work. However, those tests are understood to be elementary and
are often not taken individually or under realistic conditions.90 Crime labs oﬀer a model
for more accurate policing, even though they themselves traditionally have fallen short of
the independence, oversight, and quality controls in clinical and scientiﬁc laboratories out-
side the criminal system. Far more rigorous regulation of crime labs and forensic evidence
is needed, and such a model oﬀers lessons for how to improve policing more generally.
The National Academy of Sciences summarized the state of aﬀairs facing forensics in
the United States in 2009: “Forensic science facilities exhibit wide variability in capacity,
oversight, staﬃng, certiﬁcation, and accreditation across federal and state jurisdictions.”91
“Rigorous mandatory certiﬁcation and accreditation programs, adherence to robust per-
formance standards, and eﬀective oversight”92 are lacking. Moreover, what policies labs do
have may be nonpublic.93

In contrast, public regulations for medical laboratories have developed over time to
support public health goals. After World War II, medical laboratories that conducted
an experiment to assess clinical labs in Pennsylvania found serious errors, such as failure
to correctly identify diseases. In 1967, Congress passed the Clinical Laboratory Improve-
ment Act (CLIA) to ensure that medical labs conduct accurate tests.94 A second wave of
reform began in the mid-1980s, after reporters at the Wall Street Journal wrote about mis-
diagnosed cancer and lax standards at labs in a Pulitzer Prize–winning series.95 In 1988,
Congress passed amendments to the CLIA extending the regulations to practically all clin-
ical laboratories, public or not. The law required that proﬁciency testing reﬂect “to the
extent practicable . . . normal working conditions” to make tests realistic.96 The law also
permitted “announced and unannounced on-site proﬁciency testing of such individ-
uals.”97 After all, the lawmakers concluded, “regular proﬁciency testing [is] vital evidence
of a laboratory’s competence.”98

91
92
93

94
95

96
97
98

See PCAST REP., supra note 47, at 57 (stating that Christopher Czyryca, the president of Collaborative Testing
Services, Inc., the leading proﬁciency testing ﬁrm in the U.S., has publicly said that “[e]asy tests are favored by the
community”).
NAS Report, supra note 10, at 14.
Id. at 6.
Sandra Guerra Thompson & Nicole Cásarez, Three Transformative Ideals to Build a Better Crime Lab, 34 GA. ST.
U. L. REV. 1007 (2018).
See 42 U.S.C. § 263a (2012).
See Walt Bogdanich, Lax Laboratories: The Pap Test Misses Much Cervical Cancer Through Labs’ Errors, WALL ST.
J., Nov. 2, 1987, at Al.
42 U.S.C. § 263a(f )(4)(B)(iv).
See 42 U.S.C. § 263a(f )(4)(B)(iv) (2012).
See H.R. Rep. No. 100-899, at 11 (1988), reprinted in U.S.S.C.A.N. at 3831; S. Rep. No. 100-561, at 3–4 (1988).

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The swift responses by federal lawmakers to clinical lab failures was completely diﬀer-
ent from the tepid responses to crime lab failures. We need similarly serious federal leg-
islation and quality controls imposed on crime labs. At the state level, there are a few state
forensic science commissions, but only the Texas Forensic Science Commission has done
audits and investigations in even a modest way.99 Maryland began licensing crime labs in
2007 after a discredited state police ballistics and ﬁrearms expert was found to have fal-
siﬁed his academic credentials, resulting in a review of over 4,000 cases.100 In response,
Maryland adopted a model based on the CLIA, extending clinical regulations to crime
laboratories.101 The statute and accompanying regulations provide a model for detailed
regulation of crime laboratories; however, the eﬀectiveness of the regulatory body that en-
forces the statute and accompanying regulations is unclear, and problems have persisted,
including in ﬁrearms examinations, which had originally prompted the regulations.102

As a result of the nonexistence of federal quality controls, many crime laboratories
have long “lacked quality control measures that would have detected” uses of scientiﬁcally
“questionable evidence.”103 No federal or national accreditation system exists in the United
States. Some states have required that their labs be accredited; otherwise, accreditation is
voluntary.104 The National Commission on Forensic Science strongly recommends that
all forensic science service providers (FSSPs) become accredited to promote compliance
with industry best practices, promote standardization, and improve quality of services.105
The American Bar Association, similarly, has made this recommendation: “Crime labora-
tories and medical examiner oﬃcers should be accredited, examiners should be certiﬁed, and
procedures should be standardized and published to ensure the validity, reliability, and
timely analysis of forensic evidence.”106 Accreditation has become far more common among

99
100

For an overview, see GARRETT, AUTOPSY OF A CRIME LAB, supra note 11, at 201–03.
Steve Lash, Maryland High Court Lifts Attorneys’ Diligence Burden in Fraudulent Ballistics Expert Appeals, MD.
DAILY REC. ( June 9, 2021), https://thedailyrecord.com/2021/06/09/md-high-court-lifts-attorneys-diligence
-burden-in-fraudulent-ballistics-expert-appeals/; Jennifer McMenamin, Police Expert Lied About Credentials,
BALT. SUN (Mar. 9, 2007, 3:00 AM), https://www.baltimoresun.com/maryland/ bal-te.md.forensics09mar09
-story.html.

101 MD. CODE ANN., HEALTH–GEN. § 17-2A ( West 2022); for accompanying regulations, see MD. CODE REGS. 10.51.00-

102

103
104
105

106

07.
See, e.g., Justin Fenton, ‘Serious Questions’ Raised by Reports on Problems Inside Baltimore Police Crime Lab,
BALT. SUN (Aug. 16. 2021, 2:18 PM), https://www.baltimoresun.com/news/crime/bs-md-ci-cr-crime-lab-folo
-20210816-u6sbc72o25gjvfqeex4mfp2kvi-story.html.
Id.
See, e.g., OKLA. STAT. ANN. tit. 74, § 150.37 (“[A]ll forensic laboratories . . . shall be ASCLD/LAB accredited.”).
NAT’L COMM’N ON FORENSIC SCI., UNIVERSAL ACCREDITATION 1 (2016), https://www.justice.gov/archives/ncfs/page
/ﬁle/624026/download.
See ABA CRIMINAL JUSTICE SECTION, ACHIEVING JUSTICE: FREEING THE INNOCENT, CONVICTING THE GUILTY 47 (Paul
Giannelli & Myrna Raeder eds., 2006).

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crime laboratories.107 This is a good step to ensure that minimal standards exist on paper,
but accreditation does not ensure that reliable and consistent work is done in practice. Thus,
the American Bar Association called for “demanding written examinations, proﬁciency test-
ing, continuing education, recertiﬁcation procedures, an ethical code, and eﬀective disciplin-
ary procedures” for all forensic analysts.108 Scientists and lawyers have called for
comprehensive quality controls for laboratories in the criminal legal system, where a per-
son’s life and liberty are at stake, but so far none have been established.

CONCLUSION

The central problem in forensics is that the function has been treated as a law enforcement
rather than scientiﬁc function. The result has undermined both public safety and fairness.
Innocent people have been convicted, and guilty people have gone free. Quality control
failures have caused enormous harm to criminal investigations, victims, and the lives of
persons wrongly convicted. We should not allow untrained oﬃcers to collect and poten-
tially alter or contaminate evidence at crime scenes instead of enlisting trained scientists.
We should not allow people to be arrested and incarcerated based on largely unregulated
forensic tests that have never been scientiﬁcally tested. Law enforcement should neither
run crime labs outright nor otherwise direct and inﬂuence lab work. These reforms also
provide a model for police more broadly. These standards will likely have to come from
lawmakers and not from the courts, which have provided little guidance regarding sound
evidence collection during criminal investigations. Fortunately, there are good models for
policing forensic evidence, including from labs that have made large-scale changes and
from clinical laboratories. Independence, accuracy, and oversight of forensic evidence
when it is handled by police, medical examiners, and crime laboratory staﬀ have the po-
tential to dramatically improve the quality of justice in the United States.

107
108

DUROSE ET AL., supra note 36.
See ABA CRIMINAL JUSTICE SECTION, ACHIEVING JUSTICE, supra note 106, at 47.

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