(This story was originally broadcast on Sept. 19, 2009. It was updated on Aug. 20, 2010.)
In the spring 2009, Boston was a city at peace.
But then, on April 10, everything changed. The "Craigslist Killer" began his seven-day crime spree.
His first victim was a woman from Las Vegas who was fleeing that city's crackdown on vice.
"I just picked a city and went to it. I've been doing it for the past two years," Leffler said of choosing Boston. Her line of work? "I was escorting."
In this case, a traveling escort. Trisha Leffler, 29, checked herself into the Westin Copley Place Hotel. No surprise, she went right to where the money is - the Back Bay area of the city, known for its fancy hotels, exclusive boutiques and hip restaurants.
When asked how much money she can make in this field, Tricia told "48 Hours Mystery" correspondent Peter Van Sant that being an escort is quite lucrative - she can make thousands of dollar a week.
Tricia said she immediately went online to Craigslist, the Web bulletin board, and placed an ad in the erotic services section. She said after submitting her ad with the headline "Sweet Blonde," she started getting phone calls right away.
"What Craigslist does is basically provide services and these prostitutes have been providing services for years. And if it's not the Yellow Pages, it's gonna be Craigslist. They find a means to advertise their services," according to Joe Moura, a Boston-based private investigator and "48 Hours" consultant.
Moura said that by acting as her own boss, Tricia was increasing her risk.
"If there's a street prostitute, she's gonna have a pimp down the street or across the street on the corner who's protecting her. Somebody using Craigslist getting a fancy hotel in Boston, she's on her own."
But that April night, when Tricia saw the man who answered her ad, she said she felt perfectly safe. "He looked nice, he looked young. Good looking, obviously."
Once the door was closed, this good-looking young man pulled out a very dangerous-looking gun.
"I backed up a little bit. He just said, 'If you do everything you're asked, no harm's gonna come to you.' He said, 'Lay down, put your hands behind your back.' When he started to walk towards me, he put the gun back in his pocket."
The man put on some black leather gloves and took out some plastic zip ties.
In an exclusive interview with "48 Hours Mystery," Tricia explained, "He knelt down with one knee in between my legs. I'm thinking like what does he want? I'm shaking. I'm scared. It dawned on me later that he could have very well killed me."
Tricia's attacker wanted money. "I had about $800 in cash, he grabbed that, put that in his pocket," she said.
As he took her credit and debit cards, Tricia said he made no attempt to disguise his face. But he was intent on getting his phone number off her cell phone.
"Was he wearing his gloves when he did that?" Van Sant asked Tricia.
"No," she replied.
"Well, how dumb is that?"
Dumb, and, as it turned out, he was more than a little weird.
He picked up a pair of Tricia's underwear from the floor and put them in his pocket. "If he would've looked at my face, it would've been, like, "What the hell are you doing?"
At that point, she explained, the gunman began walking around the hotel room looking for something.
"And he said, 'Come here.' And I went in to the bathroom and he basically tied me to the doorknob. I got really scared. He took a knife out of his pocket and cut the phone lines. He came back over to me and taped my mouth. He put three pieces of tape over my mouth."
Tricia noticed that he had yet to put the gloves back on, meaning that his fingerprints were all over that tape.
After he left the room, she quickly broke free from the zip ties, but worried that he may still be nearby.
"I'm worried he's listening through the door. I look out the peephole. There's nothing - there's nobody out there. I open the door very slowly, stuck my head out, looked both ways. Nobody was in the hallway. I crept down the hall to see if he was maybe standing by the elevator. [There's] nobody by the elevator.
"I'm still shaking. I'm still nervous," she continued. "So I went back to the room, grabbed my room key, shut the door and went and knocked on the next-door neighbor's door.'Can I call security? I've just been robbed at gunpoint.'"
From the start, Boston police took Tricia Leffler seriously.
"They didn't say, 'You're not supposed to be doing this' - anything like that. They were very respectful towards me. They wanted to catch the guy," she told Van Sant. "The next day, when I went down to the police station to look through some photos, they had a surveillance photo of the man that I described."
Stills taken from a hotel security camera were the first shots of the man who became known as the Craigslist Killer.
Van Sant asked Joe Moura, a private investigator, "Wasn't he aware that there were security cameras that people could track him down if something did go wrong?"
"Sometimes, because there's security cameras everywhere, it's almost like they're not there. He figured the crime was so bold, he was gonna walk out, she's not reporting it, nobody's gonna be checking video if he was here or not. He figures it's a clear-cut case. He's outta here," Moura explained. "The thing about this young lady is that she did come forward and actually helped in the investigation."
Tricia remained in Boston, waiting for the police to release her cell phone. On April 15, they called. "We need to talk to you. It's really important," she recalled. "Five minutes later, [there's] a knock at the door. And then they handed me a photograph. And I said, 'Wow, this is a really good picture of him. Where did you get it from?' And they just stopped and looked at me and they were, like, 'Is that him?' I said, 'Yeah, this is him. Was this before he came up to my room?'
"They said, 'No, this is taking from a different hotel.' And they said.' He murdered another girl last night.'"