The CBS News magazine program "48 Hours" has an exclusive interview with Trisha Leffler, who says she was Markoff's first victim.
Leffler told "48 Hours" she believes she is lucky to be alive after Philip Markoff pulled a gun on her when he answered her erotic service advertisement on Craigslist.
Leffler said, "I shut the door, I turned around and I locked it. That's when he pulled out the gun."
Police say Markoff was addicted to Web sites specializing in sex, pornography and fetishes.
Criminologist Casey Jordan told CBS News, "He was absolutely convinced that no one would ever suspect that he would have a double life, that he would actually answer ads for sex workers or erotic dancers."
But his propensity towards violence was never evident, they say until the night he tied up Leffler, and robbed her at gunpoint.
Leffler said, "It dawned on me later that he could have killed me."
But just four days later, police say that's just what he did to Brisman.
Paul LaRosa of "48 Hours" and co-author Maria Cramer, a Boston Globe journalist, appeared on "The Early Show" Thursday discuss their new book "Seven Days of Rage: The Deadly Crime Spree of the Craigslist Killer."
Read an excerpt
On Saturday, September 19, at 10 p.m. ET/PT LaRosa's "48 Hours" special on the Craigslist killer will air.
Watch a preview
LaRosa said Markoff "had a lot going on" in his life around the time Brisman died.
"He had a lot of sexual profiles online that no one knew about. We sort of reveal them now for the first time in the book and this broadcast on Saturday night, '48 Hours.' But nobody knew about him. His fiance who lived with him didn't know about them I mean, he kept it well hidden as a lot of people do."
"Early Show" co-anchor Harry Smith commented that Markoff seemed to be a high-profile guy who was in medical school. Smith said there seemed to be quite a dichotomy in his life.
LaRosa said, "One psychiatrist I spoke to said that could lead to a fractured identity, that this completely split personality could create, in the end, violence. And it seems like it did."
LaRosa added Markoff clearly had an interest in bisexuality, bondage and S&M. However, he was planning to get married.
"That's a big split in your personality," he said.
But what about Markoff's fiancé? Did she have any clue?
Cramer said she was in the dark about Markoff's double life. Cramer said, "According to the detectives that I spoke with that interviewed her, she had no idea what was going on. And if anything, she was often not in Boston, she was at her home in Jersey planning her wedding and taking care of a back condition that she has, so she wasn't around very often to see what Phillip might have been up to."
LaRosa added that the clock was literally ticking for Markoff. The couple had a wedding Web site that featured a countdown clock that was ticking off time until the couple was to say, "I do."
"There seemed to be a lot of pressure on Phillip," LaRosa said. 'The wedding was impending, he loved to gamble, he had the secret life, he was in medical school, let not forget that. There's a lot of stuff going on in his life."
LaRosa added . He clearly had an interest in by sexuality, bondage, S and M. On the other hand, he's getting married to this beautiful young woman from new jersey. That's a big split in your personality.
Markoff has pleaded not guilty in this case. His trial is scheduled to start in June 2010.