CODIS is the acronym for Combined DNA Index System. It is a database developed by the FBI in 1998 containing the DNA profiles collected from criminal offenders. When a crime is committed, an investigator can submit the DNA profile obtained from evidence into the database to search for the individual who is likely to have committed the crime. DNA evidence did not become useful in criminal investigation until the early 1990s, and with the invention of the database, law enforcement agencies were able to broaden the pool of potential suspects. However, because Joseph DeAngelo’s DNA was not on file in CODIS, it was not useful in solving the Golden State Killer case.

A cold case is a crime that remains unsolved and is not actively being investigated by law enforcement. Several factors can cause a case to go cold, such as lack of evidence, lack of leads, lack of resources, or more pressing cases that must take precedence. Holes becomes driven to solve the East Area Rapist (EAR) cold case when he stumbles on it in 1994, and through EAR, he discovers his passion for examining cold cases in general. Overall, Unmasked suggests that as The Human Impact of Crime is not time-limited, neither should the investigation of these cases be.