Cold case refers to a crime or accident that has not been solved and is not the subject of current criminal investigation or civil litigation, but for which new information could emerge from new witness testimony or re-examined archives, as well as retained material evidence. New technical methods developed after the case can be used on the surviving evidence to re-analyse the causes, often with conclusive results.

Violent or major crime

Typically, cold cases are violent or other major felony crimes, such as murder or rape which unlike unsolved minor crimes are generally not subject to a statute of limitations.

Sometimes disappearances can also be considered cold cases if the victim has been not seen or heard from for some time such as the case of Natalee Holloway.

Other cases are cold when the crime, usually through discovery of human remains, is discovered well after the fact. Other cases are classified cold cases when a case that had been originally ruled an accident is re-designated a murder when new evidence emerges.

Some cases become instantly cold when a seeming closed (solved) case is re-opened due to the discovery of new evidence pointing the way from the original suspect(s). This happens in a surprising number of cases, and is the result of a miscarriage of justice. The John Christie murders are a classic case, when Timothy Evans was wrongly executed for the alleged murders of his wife and child. Many other bodies were later found in the house where they lived with Christie, and he in turn was executed for those crimes. The case helped a campaign aginst capital punishment in Britain.

Identifying a suspect

A case is considered unsolved until a suspect has been identified, charged, and tried for the crime. A case that goes to trial and does not result in a conviction can also be kept on the books pending new evidence.

Many times, those investigating the case have a suspect in mind or he/she emerges early in the investigation but have not been able to find evidence sufficient to charge the suspect with the crime -- especially since most suspects are not forthcoming with a confession.

Even in other cases a suspect never even considered before or even unknown emerges mainly through forensic or DNA evidence. This is usually the case in brutally violent homicides where a suspect is either bludgeoned to death or in which rape or sexual assault is the underlying crime. Sometimes forensic evidence even helps to determine the crimes are serial crimes. The BTK case and Original Night Stalker (still unsolved) cases are such examples.

Notable Examples

• In 2005 Edmond Jay Marr pleaded guilty to 2nd degree murder to the March 1983 kidnap and murder of Elaine Graham, 29, a nurse and student at California State University at Northridge. He became a suspect when acquaintances noted that he was in the immediate area of her disappearance and was seen at a sister's home only a few blocks where the victim's car was found. A knife found in the suspect's possession (when he was arrested for armed robbery a month later) was later proven to be the murder weapon when DNA evidence, unavailable in 1983, provided by Elaine's daughter matched blood found in the knife's crevices.