In September 2004, the department's crime lab matched male DNA taken from both the McKeown and Sokoloff crime scenes, police said. But they couldn't match the DNA to a suspect. Over the next five years, detectives developed 14 suspects, but their DNA ruled each of them out as the attacker.
The break came last October, when two officers collected DNA from Thomas as part of an ongoing process to swab registered sex offenders. On March 27, the California Department of Justice DNA Laboratory notified detectives that his DNA matched the evidence from the Sokoloff slaying.
On March 31, they were told that his DNA matched the four other slayings. He was arrested later that day. Thomas is being held at L.A. County Jail and could not be reached for comment.
Police said that connecting the dots in such cases was much harder before DNA and computer databases.
"It was harder to make connections," said LAPD Deputy Chief Charlie Beck. "The difference in investigative techniques, communication and the science is huge."
It has become standard practice for investigators to collect evidence such as hair, fingernail scrapings, and bodily fluids from murder and rape victims.
DNA databases have contributed to a number of arrests and convictions since the beginning of the decade. Several years ago LAPD detectives arrested Chester Dewayne Turner, who was responsible for 10 rape-strangulations along the Figueroa Street corridor in South L.A. and in downtown.
He was convicted of the murders and sentenced to death in May 2007.
But the technology is limited unless a perpetrator's genetic code lands in the database.
The LAPD is still investigating at least a dozen murders, over a span of two decades, connected to an unidentified serial killer dubbed the "Grim Sleeper."