A cold case is any criminal investigation by a law enforcement agency that has not been solved for (generally) at least one year and, as a result, has been closed from further regular investigations. A cold case may be closed for various reasons such as: previously available technology was not able to adequately analyze the evidence in order to form a conclusion; witnesses were hostile and uncooperative; various time constraints hindered the investigation; the originally assigned detectives had a heavy workload; a lack of worthwhile leads stalled the case.
Almost assuredly, every law enforcement agency in the United States and in foreign countries has cold cases on their books that could be reopened and solved. However, since agencies have limited amounts of manpower and resources, usually only the most terrible cold cases such as violent crime are reopened. Plus, violent crimes such as homicides and sexual assaults are well matched to being reopened as cold case reviews because such cases generally produce the most evidence. However, the decision to reopen a cold case is also dependent on many other factors including: the overall severity and cruelty of the crime; cooperativeness, whereabouts, and number of witnesses; age of the crime; amount and condition of the inventory (including physical evidence ) relevant to the case; whereabouts of previously identified suspects; and new technologies and tools that may help to determine evidence previously unable to be solved. Oftentimes, cases are reviewed and prioritized according to the likelihood of an eventual solution, with the highest priority cases given to those in which new witnesses, information, and evidence can now identify suspects.
Usually only the most talented and experienced law enforcement investigators are assigned to cold cases because of the thoroughness, persistence, and high motivation necessary to review the large numbers of detective notes, patrol reports, photographs, electronic information, laboratory documents, crime scene drawings and diagrams, witness lead sheets, and suspect information. Important characteristics required of cold crime members include: strong communication and interpersonal skills, seniority, strong research skills and deductive reasoning, creativity, patience, and enthusiasm. Sometimes a special "Cold Case Squad" may be organized, either temporarily or permanently, to deal solely with cold cases, especially when current cases prevent such older cases from being worked. In nearly all scenarios, cold case investigations present many varied and intense challenges to any law enforcement agency.
see also Cold hit; Physical evidence.