DNA evidence exceptions to statutes of limitations give prosecutors extra time to charge a crime once genetic testing identifies a suspect, and they let prosecutors file charges against an unnamed DNA profile before any deadline runs. At the federal level, 18 U.S.C. § 3297 opens a new prosecution window equal to the original limitations period as soon as DNA testing points to a specific person. Most states have enacted their own versions. None of these rules, however, can bring back a case whose original clock had already expired before the exception was enacted.
When No Exception Is Needed
Some crimes have no deadline at all, so DNA exceptions never come into play. Under 18 U.S.C. § 3281, any federal crime punishable by death can be prosecuted at any time.1Office of the Law Revision Counsel. 18 USC 3281 – Capital Offenses Murder is the clearest example. Evidence collected at a 1980 crime scene remains legally viable for a 2026 prosecution without any special provision.
Federal law also stretches the window for crimes against children. Under 18 U.S.C. § 3283, offenses involving the sexual or physical abuse of a child under 18 can be prosecuted during the victim’s lifetime or for ten years after the offense, whichever is longer.2Office of the Law Revision Counsel. 18 USC 3283 – Offenses Against Children Many states have gone further and eliminated time limits entirely for serious sexual offenses. In those categories, DNA matters as an investigative tool, not as a legal prerequisite for bringing charges.
How 18 U.S.C. § 3297 Extends the Federal Clock
The main federal DNA exception doesn’t pause the limitations clock while a suspect is unknown. It creates a second prosecution window that opens after DNA testing identifies a specific person, equal in length to the original limitations period for the crime.3Office of the Law Revision Counsel. 18 USC 3297 – Cases Involving DNA Evidence
The default federal statute of limitations for non-capital felonies is five years.4Office of the Law Revision Counsel. 18 USC 3282 – Offenses Not Capital Say a federal burglary occurs, biological evidence is recovered, and no suspect surfaces for eight years. The original five-year window has already closed. But if DNA testing then implicates a specific individual, § 3297 gives prosecutors a fresh five years from the date of that identification to bring charges.
Two features of this rule deserve attention. First, it applies to any federal felony. There is no limitation based on whether the crime was violent, financial, or something else; the statute draws no such distinction.3Office of the Law Revision Counsel. 18 USC 3297 – Cases Involving DNA Evidence Second, the structure guarantees a full new period regardless of how much original time remained. If the five-year clock had one day left at the moment of the DNA identification, prosecutors still get a complete five years.
The identification date is what starts this new window, so the laboratory’s formal match confirmation becomes the key legal moment. Defense attorneys will scrutinize when, exactly, the identification occurred and whether the prosecution filed within the resulting deadline.
John Doe DNA Indictments
A different strategy avoids the timing question altogether by starting the prosecution before the suspect’s name is known. Prosecutors file an indictment that identifies the defendant by their unique genetic profile rather than a legal name.5National Institute of Justice. Killing Time: The Application of John Doe Indictments to Keep Cases Warm Filing within the original statutory window satisfies the legal requirement to bring charges on time.
Courts have broadly accepted the approach. The reasoning is that a DNA profile identifies a person with far greater precision than a name or physical description, satisfying both the constitutional particularity requirement and the notice function of an indictment.6Sexual Assault Kit Initiative. Understanding the Use of John Doe Arrest Warrants in Prosecuting Cold Case Sexual Assault for Prosecutors Federal Rule of Criminal Procedure 7 permits an indictment to omit the suspect’s identity when it is unknown, provided the charging document otherwise describes the essential facts of the offense.7Cornell Law School. Federal Rules of Criminal Procedure Rule 7 – The Indictment and the Information
Once filed, the attached arrest warrant stays active indefinitely. Law enforcement can serve it the moment the genetic profile is matched to a named person through the FBI’s Combined DNA Index System (CODIS). This approach is especially common in sexual assault cases where biological evidence is recovered but no suspect is immediately identified. The one practical limitation is that prosecutors need a usable DNA profile to file the indictment. A degraded sample that cannot produce a reliable profile closes off the option.
State Discovery Rules
Most states have enacted their own DNA-related exceptions, and the approaches vary. Some use a discovery rule that pauses the limitations clock entirely from the moment a profile is developed from crime scene evidence until the profile is matched to a named person. Others grant prosecutors a fixed window after identification to bring charges. A handful have eliminated statutes of limitations altogether for certain categories of sexual assault, which moots the DNA question for those offenses.
The trend over the past two decades has been toward longer windows and broader exceptions, driven largely by the sexual assault kit backlog. The rules that apply depend on where the crime occurred, not where the suspect is eventually found or where the DNA match is processed. Defense attorneys routinely challenge whether the applicable state exception was properly triggered, including whether the profile was developed through accredited laboratory procedures and whether the prosecution acted within any secondary deadline the state imposes.
The Ex Post Facto Limit
Every DNA exception runs into one constitutional wall. In Stogner v. California, the Supreme Court held that a law cannot retroactively revive a prosecution that was already time-barred when the new law was enacted.8Justia Law. Stogner v California, 539 US 607 (2003) If the original statute of limitations ran out before a jurisdiction enacted its DNA exception, the case stays dead no matter how strong the genetic evidence turns out to be.
Consider a state that originally gave prosecutors six years to charge sexual assault, then later passed a law eliminating the deadline when DNA evidence is available. If the six years expired before the new law took effect, prosecution is barred. The Constitution treats a retroactively extended limitations period as an increased punishment imposed after the fact.
The reverse situation is different. If the original limitations period had not yet expired when the new DNA exception was enacted, the extension generally applies to that case. Legislatures can lengthen or eliminate a deadline for crimes still within the original prosecution window. This is why the timing of state DNA legislation matters so much for cold cases, and why some otherwise solvable cases remain permanently beyond reach.
Why These Exceptions Exist
The practical reason for DNA tolling rules shows up most clearly in the untested sexual assault kit backlog. A 2021 study estimated that between 300,000 and 400,000 sexual assault kits went unsubmitted to laboratories between 2014 and 2018, and a separate 2018 study estimated approximately 200,000 untested kits remained in police custody.9Congress.gov. Sexual Assault Kits (SAKs) and the Backlog of Untested Sexual Assault Kits Each untested kit represents a potential identification that never happened within the original prosecution window.
In many of those cases, even if testing today produced a match, the limitations period has expired and Stogner blocks revival. That reality has pushed states to reform in two directions at once: extending or eliminating time limits for sexual assault prospectively, and funding kit-testing initiatives to generate matches before existing deadlines run out. John Doe indictments have been used aggressively to preserve cases where a profile exists but backlog prevented a timely identification.
What a DNA Exception Doesn’t Fix
Keeping a case within the limitations period is not the end of the inquiry. Even when § 3297 or a state equivalent gives prosecutors a valid window, defendants can still attack the delay and the evidence itself.
Pre-Indictment Delay and Due Process
The Sixth Amendment speedy trial right doesn’t attach until a person is formally charged or arrested, so the years a profile sits unmatched in CODIS usually don’t count against the government under that framework.10Cornell Law School. Reason for Delay and Right to a Speedy Trial A separate due process challenge can target the gap between the crime and eventual charges, but courts generally require the defendant to show actual prejudice, such as a lost alibi witness or destroyed exculpatory evidence. Vague claims about faded memories typically aren’t enough. Some courts also require a showing that the government deliberately delayed to gain a tactical advantage. In DNA cold cases, prosecutors can usually point to the legitimate explanation that the suspect was literally unknown until the database match, which tends to defeat these challenges.
Chain of Custody and Lab Standards
Biological evidence degrades when exposed to heat, moisture, or contamination. Federal guidance recommends that biological evidence in open investigations be retained indefinitely for homicides and for the length of the statute of limitations for other offenses.11National Institute of Standards and Technology. NISTIR 7928 The Biological Evidence Preservation Handbook Actual storage conditions in underfunded evidence rooms often fall short. Defense teams can challenge breaks in the chain of custody, improper storage, contamination, degradation, or mislabeling. State laws on mandatory retention vary widely, and some states have no specific statutory requirement at all.
For a profile to enter CODIS and generate the match that triggers these exceptions, it must be processed by a laboratory that meets the FBI Director’s Quality Assurance Standards and holds accreditation from a recognized forensic science organization.12Federal Bureau of Investigation. Quality Assurance Standards for Forensic DNA Testing Laboratories Laboratories that outsource to private vendors must ensure those vendors also comply. In cases spanning decades, the laboratory that originally processed the evidence may have changed hands, lost records, or used methods that have since been superseded, each of which gives the defense an angle to challenge the match that opened the prosecution’s new window in the first place.