General · EdgepediaSeptember 17, 20268 min read

Cold case

A cold case is a criminal investigation, most often a homicide or a missing or unidentified person case, that remains unsolved after investigative leads have been exhausted or a jurisdiction's designated period has elapsed. There is no universal legal definition: the US National Institute of Justice (NIJ) Cold Case Working Group uses three years, some jurisdictions use one or five years, and others classify a case as cold only when no further investigative steps can be identified.¹

Key fact	Detail
Definition	No universal definition; NIJ uses a violent crime, missing person, or unidentified person case unsolved at least three years with potential to be solved through new information or advanced evidence analysis¹
US unsolved homicides	More than 242,000 per a UCR-based NIJ estimate; the Murder Accountability Project counts 34 percent (roughly 331,000) of homicides reported 1965–2020 as unsolved¹^•²
Clearance trend	US homicide clearance has declined from 78.3 percent in 1975¹
Dedicated units	Only 7 percent of surveyed US departments maintain dedicated cold case units; 18 percent of departments with 100 or more officers, 1 percent of those with 50 or fewer¹
Success rates	About one in five cold cases cleared, one in 20 investigations resulting in arrest, one in 100 resulting in conviction³
Key forensic driver	Forensic investigative genetic genealogy (FIGG) develops leads when conventional DNA and CODIS searches do not identify a suspect⁴
UK practice	Unsolved murders are never officially closed; investigative effort simply stops unless further information becomes available⁵

Definition and scope

In general usage a cold case is simply a police case that has not been solved.⁶ Procedurally, the term is defined differently across jurisdictions. Some consider a case cold when investigative leads have seemingly been exhausted; others apply a fixed elapsed time of one, three, or five years.¹ Department policies range from three months to one year depending on department size and the number of homicide detectives.⁴ Washington DC's Metropolitan Police Department transfers unresolved cases to its Major Case/Cold Case Squad after no further investigative steps are identified and up to four years have elapsed.¹

The NIJ Cold Case Working Group's working definition covers a violent crime, missing person, or unidentified person case unsolved for at least three years that has the potential to be solved through newly acquired information or advanced technologies to analyze evidence.¹ In the United Kingdom there is no official definition or set point in time when an investigation goes cold; a case becomes cold when all viable leads are exhausted and the Senior Investigating Officer considers nothing further can be progressed. The UK instead uses the term "long-term case" for one open twenty-eight days or longer.⁵^•²

Cold cases overlap with two related categories: missing person cases and unidentified remains. In February 2019 the NamUs database listed 27,927 active missing and unidentified persons cases, including about 5,163 unidentified persons cases, of which 48 percent had an undetermined manner of death, and 1,945 of 15,444 open missing persons cases marked as foul play.¹ In the UK there are over 5,000 unsolved missing person cases more than one year old and over 1,000 unidentified body cases.²

How cases go cold and get reopened

Under Ohio BCI's definition, a cold case homicide is an investigation reported to law enforcement that remains unsolved after all significant and viable leads have been exhausted.⁷ In the UK, unsolved murders are never officially closed; investigative effort simply stops unless further information becomes available. UK practice distinguishes "undetected" cases, in which no suspect was identified, from "unresolved" cases, in which a conviction was overturned.⁵

Reopening. Cases are reopened when new information comes to light, witnesses provide new information, or an offender confesses.⁵ Reopening typically begins with mining case files from sources beyond the originating agency, such as retired investigators, crime labs, medical facilities, and prosecutor and coroner offices, then reorganizing evidence, updating witness and suspect identifications, and preparing a new case synopsis.⁷ Cold case detectives reassess previously collected evidence for usability, speak with the original investigators, obtain missing notes from the case file, and reinterview old witnesses.⁴

Cold case units and review processes

Dedicated units are rare. A national survey of 1,051 US law enforcement agencies found only 20 percent had a protocol for initiating cold-case investigations, 10 percent had dedicated cold-case investigators, and 7 percent had a formal cold-case unit.³^•⁸ Among departments with 100 or more officers the dedicated-unit share rises to 18 percent; among those with 50 or fewer officers it is 1 percent. Very few of the roughly 18,000 US agencies have units, largely because of a lack of financial resources and a lack of formal protocols for initiating cold case investigations.¹

Where units exist, cases are referred to cold case squads by homicide supervisors or prosecutors and prioritized by likelihood of being solved.⁴ Reviews usually draw on several disciplines: a group goes through the case file together with every piece of physical, digital, and investigative proof that exists, and may carry out advanced DNA testing, additional forensic work, and a criminal intelligence review that includes checking the case against crimes from other jurisdictions and national databases.⁷

Forensic advances and genetic genealogy

Advances in forensic technology and improved databases allow evidence once unsuitable for testing to yield probative leads in older cases.¹ In the UK, the crimes most likely to receive cold case review are murder and stranger rape, driven in part by forensic advances: upgraded crime scene samples from historic cases have matched profiles already held on the National DNA Database (NDNAD), identifying previously unknown offenders.⁵

The key recent technological development is forensic investigative genetic genealogy (FIGG), which uses detailed genetic information and genealogical research to develop leads when conventional DNA and Combined DNA Index System (CODIS) searches do not identify a suspect.⁴ Amateur sleuths increasingly generate leads using DNA databases, social media, and true-crime podcasts, including genetic genealogy databases to find suspects whose DNA is not in criminal databases; popular-culture interest in cold cases has grown over the past two decades through podcasts, documentaries, best-selling books, and conventions such as CrimeCon.⁴^•²

By the numbers

Unsolved homicides. Based on FBI UCR data, experts estimate more than 242,000 unsolved homicides in the United States.¹ The Murder Accountability Project reports a different figure: 34 percent, roughly 331,000, of US homicides reported between 1965 and 2020 as unsolved.² Ohio's Bureau of Criminal Investigation cites a further accumulation figure: since 1995, more than 100,000 cold case homicides have accumulated in the United States.⁷

Clearance decline. The US homicide clearance rate has declined since 1975, when it stood at 78.3 percent.¹ FBI UCR data for 2016 show an estimated 15,566 homicides with a 59.4 percent clearance rate, within 1,183,933 violent crimes cleared at 45.6 percent overall; aggravated assaults were 53.3 percent cleared, sexual assaults 36.5 percent, and robberies 29.6 percent.¹

Cold case outcomes. Respondents to the national survey estimated that about one in five cold cases are cleared, one in 20 cold-case investigations result in arrest, and one in 100 result in conviction.³ Higher cold-case clearance rates were associated with agency funding level and access to investigative databases.⁸

Funding. Only 20 percent of cold-case work is funded through line items in agency budgets; most is funded by grants or supplemental funds.³^•⁸

How it compares

Cold cases clear at far lower rates than fresh ones. The 2016 UCR statistics reported a 59.4 percent homicide clearance rate, while a cold case investigation clears about one case in five and produces a conviction about one time in 100.¹^•³ Clearance also varies sharply by crime type even among fresh cases, from 53.3 percent for aggravated assaults down to 29.6 percent for robberies.¹

US and UK practice differs structurally. US agencies decide case by case whether to maintain units or protocols, with most cold-case work grant-funded; the UK never formally closes unsolved murders and concentrates review on murder and stranger rape, where forensic database matches can reopen historic cases.³^•⁵ Outcomes in England and Wales show the same pattern of attrition: 33 percent of all initially recorded homicides between April 2018 and March 2019 saw no suspects charged, and fewer than 2 percent of rape cases result in suspects being summonsed or charged.²

Outcomes, legal and ethical dimensions

A cold case can be closed through arrest, administratively, or when the suspected offender is deceased or serving a life sentence for another crime.⁴ Even when a cold-case investigation succeeds, it often leads to no arrest: according to the RAND study, between a third and a half of successful investigations failed to produce one, sometimes because witnesses could not be found or refused to cooperate, sometimes because the suspect had died or was already in prison, and sometimes because DNA testing pointed to several people or gave no clear answer. In sexual-assault cold cases, about one third of cases with a suspect DNA match are not filed because of victim cooperation, credibility, or availability problems.³

Factors predicting cold-case success include the basis for initiating the investigation, victim and crime characteristics such as age of case, location of body, victim age and gender, progress in the initial investigation, and investigator actions such as developing a new theory of the crime.³

References

Topic: Encyclopedia › Society and history › Law and justice › Criminal law and penal justice › Crime, criminology, and criminal justice policy › Notable deaths, disappearances, and unsolved cases

Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 25, 2026 · Edited: Sep 30, 2026; Oct 25, 2026 · Last review: Oct 25, 2026

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