"We became aware of it right around April of 2007," LAPD Detective Bill Fallon told "Nightline" in March 2009. "And we realized there was a serial killer because of DNA hits we started getting. So when we get those hits, we're like, 'whoa.' That's when we started digging it."
But the police didn't notify the community until Christine Pelisek, a reporter from LA Weekly, began investigating.
"I was the one who told some of the family members that their daughters were victims of a serial killer," Pelisek said. "I mean, they didn't even know. The public safety committee, they had no idea. I mean, the police commission, I spoke to the police commission [to whom the police chief reports]. They didn't even know. So there were a lot of people very upset that the police didn't let the community know."
Fallon says investigators didn't want to alert the killer that they were searching for him.
"We wanted to get a a step ahead of the killer himself," he said. "I don't want you to know I'm coming for you until I find out who you are, where you are and what you are doing."