§ 8.04. Preservation and Retention of Evidence

Agencies should adopt policies setting out the circumstances and manner in which evidence is to be retained and preserved, both before and after adjudication, taking into account factors such as the nature of the offense, the potential probative value of the evidence, the interests of the defense and others, and storage costs.


a. Preservation. It is important to preserve all probative evidence. The U.S. Supreme Court has held that willful destruction of evidence by law enforcement violates the Due Process Clause. Arizona v. Youngblood, 488 U.S. 51 (1988). In order to further the purposes of accurate and just adjudication, however, it is essential to go further and preserve all potentially probative evidence. In this regard, the mental state of the officer in failing to preserve evidence is irrelevant.

b. Retention. It also is important that investigators and agencies not only preserve evidence when they initially collect it, but also make arrangements to retain evidence, including after adjudication is final. Evidence retention is important in the event that a case is reopened and the evidence requires analysis in the future. The federal government, and more than half of the state governments, have enacted laws that impose obligations, sometimes at the election of the defense, to preserve evidence after a criminal conviction is final. The manner of retention also should be set out in policy so that it is clear who has custody of evidence and so that preserved evidence can be located readily. Further, these policies should set out requirements to ensure that evidence is preserved under conditions that prevent it from being contaminated.

c. Considerations. Agencies should adopt policies that set out in advance their priorities and the relevant considerations for determining whether to retain and preserve evidence. These policies should require, at a minimum, that evidence be retained in the more serious criminal cases; in contrast, it may be a lower priority to collect, much less retain, evidence from crime scenes in minor cases. An important consideration is the probative value of the evidence. However, it should be emphasized that new technology can make seemingly nonprobative evidence highly probative, as occurred with the advent of microscopic DNA testing that made it possible to test evidence that might have been discarded in the past. Further, the potential for future litigation in the matter should be considered. Agencies should retain evidence in cases in which defendants request that such retention, or those in which the interests of others, such as the press or victims, could be implicated. Storage costs are a relevant consideration, particularly if special measures must be taken to prevent degradation of the evidence. Each of these considerations should be reflected in policy in order to provide guidance to law enforcement, lawyers, and the public.

Reporters’ Notes

Under the U.S. Constitution, an agency’s failure to preserve forensic evidence in a usable form for the purpose of forensic testing is not a violation of due process unless it is done in bad faith. Arizona v. Youngblood, 488 U.S. 51, 56-58 (1988). But it can be difficult to make showings of bad faith, because doing so requires an inquiry into the subjective motivations of officers. Indeed, ironically, the defendant in Youngblood was later exonerated by DNA testing of the poorly preserved evidence. Brandon L. Garrett, Convicting the Innocent: Where Criminal Prosecutions Go Wrong 196 (2011). Further, there have been growing concerns that in some jurisdictions, evidence from rape kits in sexual-assault investigations has not been carefully preserved and retained to permit forensic testing. It is important that agencies err on the side of retaining evidence, because new technologies may develop that make it possible to analyze evidence when it previously was not possible.

In response to concerns about unpreserved evidence, as well as advances in forensic testing, many agencies and states have enacted evidence-retention laws and policies. See, e.g., “Sexual Assault Victims’ DNA Bill of Rights.” Cal. Penal Code § 680(3) (2011) (“Law enforcement agencies have an obligation to victims of sexual assaults in the proper handling, retention and timely DNA testing of rape kit evidence or other crime scene evidence and to be responsive to victims concerning the developments of forensic testing and the investigation of their cases.”); D.C. Code § 22-4134 (2019) (requiring law enforcement to “preserve biological material that was seized or recovered” in cases resulting in a conviction or juvenile adjudication).

Evidence preservation and retention begins with policing agencies, which collect the evidence in the first instance. Uniform standards are needed governing the retention and preservation of evidence by agencies. Nat’l Institute for Science & Nat’l Institute for Justice, Biological Evidence Preservation: Considerations for Policymakers (2015), https://nvlpubs.nist.gov/nistpubs/ir/2015/NIST.IR.8048.pdf.

Evidence-preservation statutes, enacted in more than half of the states, require that evidence be preserved after trial. See, e.g., Colo. Rev. Stat. § 18-1-1103 (2009); D.C. Code § 22-4134 (2019); 725 Ill. Comp. Stat. 5/116-4 (2019); 18 U.S.C.A. § 3600A (2018). Such statutes should be observed carefully by policing agencies, particularly because many of these statutes do not provide strong remedies for violations that result in the destruction of evidence. See Cynthia E. Jones, Evidence Destroyed, Innocence Lost: The Preservation of Biological Evidence under Innocence Protection Statutes, 42 Am. Crim. L. Rev. 1239, 1257-1258 (2005). But agencies also should have their own policies on evidence preservation. The coverage of state statutes is highly uneven. Many statutes limit preservation to certain types of evidence, such as biological evidence; to only certain types of cases, such as death-penalty cases; or to limited time periods, such as just while a defendant remains in custody. Thus, even in states with evidence-retention statutes, clear agency-level policy remains highly important. See Technical Working Group on Crime Scene Investigation, Crime Scene Investigation: A Guide for Law Enforcement 17-32 (2000).

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