## Why DNA Didn’t Resolve the Case Earlier
The question of why the Golden State Killer remained unidentified for so long despite the existence of biological evidence is worth addressing in specific terms, because the answer involves particular features of the evidence and the available technology at specific points in time.
The Combined DNA Index System — CODIS — was established by the FBI in 1990 and became operational in 1998. It contains DNA profiles from convicted offenders required by law to submit samples, from arrestees in states that mandate collection upon arrest, and from crime scenes in unsolved cases. As of recent reporting, the database contains several tens of millions of profiles and has contributed to hundreds of thousands of investigations.
The Golden State Killer’s crime-scene DNA was in CODIS as an unidentified profile. It was compared against profiles in the offender database. No match appeared.
No match appeared because Joseph DeAngelo had no prior convictions that required DNA submission. He had been arrested once — for petty theft, in 1979 — but that arrest did not result in a conviction that required DNA sampling under the laws of that period. The minor criminal record that ended his police career left no DNA in the system that would have been compared against the crime-scene profile.
This is the fundamental limitation of a database system that relies on prior criminal involvement as its entry criterion. An individual who commits crimes, evades conviction, and does not return to the criminal justice system’s attention in ways that require DNA collection will not appear in that database regardless of how long the database grows. The Golden State Killer’s unidentified profile could sit in CODIS indefinitely without producing a match as long as DeAngelo himself never entered the system.