Investigators searching the apartment of Philip Markoff, the accused murderer now known as the "Craigslist Killer," found a handgun and panties belonging to the two victims hidden in a hollowed-out copy of the textbook Gray's Anatomy of the Human Body, two law enforcement sources told ABC News.
Markoff appeared to be collecting women's panties, which investigators believe were "souvenirs" from his alleged victims, two law enforcement sources said.
Police have asked anyone who may have been contacted by Markoff via Craigslist to come forward, and law enforcement sources told ABC News that detectives investigating the case are now fielding calls from other potential victims.
"There could be none, there could be others," Suffolk County District Attorney Dan Conley told "Good Morning America." "We're not interested in prosecuting them for massage services."
The panties, found hidden in Markoff's apartment and was marked and bagged by police as potential evidence in the case, are one of the reasons investigators believe there could be more victims who have not yet come forward, law enforcement sources said.
Markoff is accused of robbing two women, whom he allegedly lured to upscale hotels through the Web site Craigslist, and killing one of them. He has pleaded not guilty.
Trisha Leffler, who said she was bound and robbed at the Westin Hotel in Boston April 10, told ABC's Boston affiliate WCVB that she immediately recognized Markoff as the man who'd robbed her when she saw him on surveillance photos released by police.
"I hope he will be behind bars for the rest of his life," she said.
Boston police have charged Markoff with the attack against Leffler and for the murder of 26-year-old Julissa Brisman at the Copley Marriott April 14. Both women had placed advertisements on Craigslist.
Leffler, who prosecutors said was robbed of $800, said the only reason she survived is because she didn't fight back. She said she was able to slip her ties shortly after her attacker left the room.
"I just complied with everything he wanted me to do," she said. "I didn't resist him in any way, and that's why."
Police said they believe Markoff's alleged crime spree was an effort to pay off his gambling debts.
Conley said Brisman was beaten very badly and shot three times at close range.
"This was a crime of great violence," he said. "We felt it was a very dangerous man we were looking for."
A wake for Brisman is scheduled for today in New York City.
A source close to the investigation told ABC News that Markoff opened a line of credit at Connecticut's Foxwoods Casino last week. Two days after Brisman was murdered, sources close to the investigation said Markoff hit the casino, leaving with $5,300 in his pocket. Markoff liked to play blackjack and gambled with black $100 chips, the source said.
Markoff and his fiancee Megan McAllister had a room reserved at the Connecticut casino for this Friday and Saturday nights, a source close to the investigation said.
The room was booked in both of their names, and they planned to use Markoff's accrued reward points from his gambling to help pay for it, the source said.
Markoff first applied for a Foxwoods rewards card at the end of 2008 but only went to the casino once that year. Then in March 2009 the visits "grew really frequent,'' the source said.
During his last visit to the casino on April 16, Markoff applied for a credit limit. Approval from the casino was pending when he was arrested Tuesday during a traffic stop while he was en route to Foxwoods with McAllister, the source and law enforcement officials told ABC News.
"Markoff was the gambler, she didn't really play the tables,'' said the source. McAllister did not have an account at the casino.
"He always played blackjack and used black chips. He was not a high roller. But he liked to buy in for $100 or $500,'' the source said
Markoff is also being looked at in a third attack, this one also a robbery, in a Rhode Island Holiday Inn Express where, again, a woman was tied up after placing an advertisement on Craigslist for massage services.
A search of his Quincy, Mass., apartment, prosecutors said, turned up a semi-automatic weapon along with ammunition, plastic zip ties and duct tape.
But as sure as police are that they have the right man, his fiancee told ABC News Monday that Markoff was not the person responsible for the robberies and Brisman's murder.
"Unfortunately, you were given wrong information as was the public," Megan McAllister wrote to ABC News in an e-mail. "All I have to say to you is Philip is a beautiful person inside and out and could not hurt a fly! A police officer in Boston (or many) is trying to make big bucks by selling this false story to the TV stations. What else is new?? Philip is an intelligent man who is just trying to live his life so if you could leave us alone we would greatly appreciate it. We expect to marry in August and share and wonderful, meaningful life together."
Conley said there is "very powerful evidence" that Markoff is the man on the surveillance videos and that Leffler has identified him as the man who attacked her.
Conley said it's understandable that his fiancee would want to support her loved one, but that they wouldn't charge him with such a heinous crime unless they were sure.
Even though Markoff doesn't seem to fit the profile of a typical killer -- he's a clean-cut medical student who was engaged to be married this summer -- looks can be deceiving.
Michael Welner, a forensic psychiatrist and chairman of the Forensic Panel, told "Good Morning America" today that a good education has nothing to do with a person's character.
"So much of crime is about choices," he said. "This is a situation of someone who had everything to lose," and his choices imploded his life.
Welner said Markoff may very well have gotten in over his head during Brisman's alleged murder, "and I think more evidence is going to shed light on that."
He pointed out that the alleged crimes were about money, not sex or power.
Markoff opened an account at the Foxwoods casino in 2008, but his visits to the casino increased "in March and April," leading the Cheryl, N.Y., native to apply for a credit line in early April, a source with knowledge of the investigation said.
"He went to Foxwoods frequently, including visits on April 2, 12 and 16,'' the source told ABC News. "On the 16th he left with $5,300 in winnings.''
Markoff also used his hometown New York address at 803 Cheryl Road and the Quincy, Mass., apartment he shared with his fiancee to apply for a credit line. The highest single bet Markoff made was $1,000, the source said.
"He came once in 2008, but then he was here all the time starting in March,'' the source said.
Authorities said they followed cell phone and computer records to Markoff, linking an e-mail account used to set up appointments on Craigslist with the two women who were attacked to his address in Quincy.
Markoff, dressed in khakis and a button-down shirt, did not say anything during the brief hearing. His attorney, John Salsberg, said his client was not guilty.
"Philip Markoff is not guilty. He has his family's support," he said. "All I have is words and that's not proof of anything."
Markoff's fiancee, Megan McAllister, who lived with him, told ABC News that police have got the wrong guy.
Police said they tracked Markoff down using surveillance videos at three hotels. In photos taken from hotel cameras, the man police have been seeking in connection with the crimes appears to be fixated on a BlackBerry. Investigators said that Blackberry is what led them to Markoff.
A police source close to the investigation said cops found Markoff by tracing Craigslist e-mails.
"They followed high-tech leads and old-fashioned shoe leather," Suffolk County District Attorney Dan Conley said in a news conference. "They've connected IP addresses and physical locations."
Markoff's friends and neighbors are shocked. After all, Markoff, a second-year medical student at Boston University, had no criminal history and was engaged to be married to a woman he met more than three years ago when they were volunteers in an emergency room. The university suspended Markoff after learning of the charges against him, a school spokeswoman said.
"I can't even put it into words, the disbelief I'm putting into works right now," Markoff's friend Jonathan Uva told "Good Morning America" today. "It's just a total disconnect from what we're hearing in the news."
Uva, who lives next door to Markoff in Quincy, Mass., said he went to sleep last night listening to police searching his friend's apartment.
"I'm a little unsettled, definitely," he said.
Another friend, Mike Dye, told "Good Morning America" that he'd had Markoff over to his apartment for parties and for the Super Bowl.
"I like to think I'm a good judge of character, hang out with people who are similar to myself," he said. "Didn't suspect anything like that."
"I would never believe this would be something he would do," friend Kym Direnzo said on "GMA."
Markoff's Facebook profile lists hundreds of friends who attend schools in Boston and upstate New York.
But for all the nice things they had to say about Markoff, his friends said there was a bit of mystery about him, though nothing overtly nefarious.
Friends said they didn't even know he and McAllister were engaged. Though they agreed they seemed like a nice normal couple, his friends said they thought the two were simply dating.
"He very rarely talked about himself," Uva said.
The couple's Web site, once flooded with well wishes from friends and family, is now filled with cruel postings from strangers, many directed at McAllister.
The site had detailed how they met when McAllister was a senior at the University of Albany and Markoff a sophomore. Their wedding date was set for Aug. 14.
Markoff's arrest came just hours after Warwick, R.I., police released new pictures of the man they believe is responsible for the attempted robbery of a woman at a Holiday Inn there last week.
Police in both Boston and Rhode Island have said they believe the attacks may have been carried out by the same person.
On Monday, investigators released a clear photograph of the suspect taken during the most recent attack in Warwick. A series of images show the suspect inside the Holiday Inn Express Hotel last Thursday evening, the scene of an attempted robbery of a woman.
The man seen in the pictures taken in the hotel closely resembles the man seen in a surveillance camera photo that was released after Brisman was found dead just days earlier.
Detectives have also a match among plastic zip-tie cuffs used to bind all three women. Two law enforcement sources told ABC News that the plastic restraints were being investigated after they were used to bind the hands of the victims.
"Detectives are aggressively pursuing a number of promising leads," Boston Police Department spokeswoman Elaine Driscoll told ABC News earlier today, refusing to comment on the plastic cuffs.
The man captured on a series of surveillance cameras in Boston's upscale Back Bay was a 20-something, clean-cut blond man who was seen leaving a luxury hotel where police said Brisman, a masseuse, was shot and killed just moments before in her room.
Brisman's death is the second in a series of crimes against women who police say advertised on Craigslist.
After the arrest, Craigslist CEO Jim Buckmaster issued a statement, saying, "We are very pleased to hear that the person alleged to have committed these crimes has been arrested, and we will continue to provide law enforcement agencies with any assistance necessary to prosecution of the case."
ABC News' Scott Michels contributed reporting to this story.