In an interview with NBC's "Today," Frey, whose book, "Witness For the Prosecution of Scott Peterson," comes out Tuesday, called Peterson a "pathological liar."
She said she met Peterson on a blind date in 2002 set up by her best friend. During their first date at a Japanese restaurant, Peterson arranged for them to be in a private room and told her a number of things -- including where he lived -- that turned out to be untrue.
"I had a good feeling, and a sense that I would hear from him again," Frey said, acknowledging she slept with Peterson that first night. "That it wasn't just going to be a one night stand."
Frey said she started thinking of Peterson as "Mr. Right" until he revealed he had been married -- just weeks before Laci disappeared he said he had "lost" his wife.
Frey started getting suspicious and asked a friend of hers to check Peterson out. It was at that point she learned Peterson was the same man who had been in the news, pleading for the return of his missing wife.