The candidate pool, at the start, was large. The family trees derived from the GEDmatch matches could have included hundreds of individuals who shared the genetic relationship indicated by the database results.
The narrowing process applied additional criteria. The crime-scene evidence and the behavioral record established constraints: the person responsible was male, had been an adult in California during the relevant years, was likely in his late twenties to mid-thirties during the primary crime period of 1976-1981, which meant he was probably born between roughly 1940 and 1955. Physical descriptions from witnesses during the 1970s provided some additional constraints. The behavioral profile — someone with possible law enforcement or military background — narrowed the candidate pool further.
As the family trees grew and the criteria were applied, the candidate pool shrank from hundreds to dozens to a small number of individuals who met all the criteria simultaneously. Joseph DeAngelo appeared in that small number.
He was in the right age range. He had lived in Sacramento and its suburbs during the EAR crime period. He had a law enforcement background. He had family connections that were consistent with the genealogical matches the database had returned. He was from a family with California roots consistent with the tree work.
He was not, at this point, identified as the Golden State Killer. He was identified as a candidate — one of potentially several individuals in the narrowed pool who warranted further investigation.
## The Decision to Confirm
The decision to pursue Joseph DeAngelo as a suspect required corroboration — independent evidence that would either confirm or exclude him as the person whose DNA was at the crime scenes.