Twenty-two-year-old Philip Markoff said nothing during a brief arraignment Tuesday.
Markoff is charged with murder in the death of Julissa Brisman, 26, of New York City, who was found dead April 14 at the Boston Marriott Copley Place. In addition, he is charged with kidnapping and armed robbery in a case involving another woman he met on Craigslist, the Internet's best-known classified ad site.
In that case, a 29-year-old woman from Las Vegas who advertised massage services was robbed earlier this month at the Westin Copley Hotel.
Police have also linked Markoff to a third attack that took place in Warwick, R.I., reports CBS News correspondent Daniel Sieberg. Police say a common link may be plastic handcuffs.
Prosecutors said they found a semiautomatic weapon at his home, as well as ammunition and materials exactly like those used in a prior attack.
Markoff was someone who was "preying on people who were in a vulnerable position," Boston Police Commissioner Ed Davis said.
The brutal portrayal is a far cry from the fun-loving photos on Markoff's Facebook page and a Web site celebrating his summer wedding plans, Sieberg reports.
Markoff faces charges of armed robbery, kidnapping and murder. His attorney, John Salsberg, did not immediately comment.
Meanwhile, Markoff's fiancée defended him Tuesday, saying "he could not hurt a fly."
Megan McAllister, in an e-mail to ABC television, said Markoff, by a Boston district attorney, is "a beautiful person inside and out" who could not have carried out such crimes.
McAllister said the couple still plan to marry in August.
Markoff has no criminal record, according to authorities.
But police believe Markoff may have been involved in other crimes against women who also posted ads on Craigslist.
"There may be other victims out there, and if you are, we want you to come forward," Suffolk District Attorney Daniel Conley said. "Our top priority is holding Philip Markoff accountable. He's a predator."
"High Tech Leads And Old-Fashioned Shoe Leather"
Police said they had long suspected that Brisman's killer was connected to a robbery at another Boston hotel.
The widely-disseminated photos released of the suspect, including new ones released early Monday, drew more than 150 tips to police hot lines.
Boston police told WBZ earlier Monday that they knew who the suspect was, but that they hadn't caught up with him yet.
They found Markoff around 4 p.m. driving in Walpole on Interstate 95, south of Boston, where he was arrested.
Private detective Joe Moura told CBS News technology correspondent Daniel Sieberg that Markoff left behind "an electronic fingerprint."
Conley told WBZ there were several pieces of evidence that linked Markoff to the two crimes, and that computer crime experts were able to connect IP addresses to physical locations.
"They've followed high-tech leads and used old-fashioned shoe leather," said D.A. Conley.
Authorities obtained a warrant to search Markoff's home. Davis would not comment if a weapon has been recovered but said more details on the investigation will be made public at the arraignment.
Boston police said they've also received more than 150 tips about Brisman's killing.
Davis said, "We are very, very happy to have this off the street in such a timely way."
Police are confident they've caught the right man, and are reaching out to other potential victims who may have been too afraid to come forward.
Police in Boston and Warwick, R.I., are working together to investigate, and while neither department has said the man seen in surveillance video committed crimes in both cities, the Chief of the Warwick Police Department, Col. Stephen M. McCartney, said that they believe there is "a strong connection between the three incidents."
Conley said police hope more possible victims who advertised on Craigslist come forward so authorities can build a stronger case against Markoff. "If you are" a victim, said Conley, "we want to help you."
Victims can call (401) 468-4200 or Boston police at (617) 343-4470, or the CrimeStoppers tip line at (800) 494-TIPS.
A "Bad Vibe"
Friends and acquaintances talking to CBS News have variously described Markoff as "likable," "preppy," politically conservative and "fun to be around."
He grew up in Syracuse, N.Y., and attended SUNY Albany as an undergraduate (Class of 2007).
A member of the College Republicans, he joined a business fraternity there.
Another alumnus of Albany who knew Markoff said he spoke of going to strip clubs but never mentioned visiting a prostitute. The same acquaintance said he got into many arguments with Markoff regarding his misogynistic attitude towards women.
The same acquaintance said girls described Markoff as "creepy" or "weird," and said they felt a "bad vibe" around him.
But others described him as "totally normal," a guy who liked to go to the average college bars or parties or just spend time hanging out with roommates.
He was engaged to be married in Long Branch, N.J., this August, according to a Web site set up to announce the couple's wedding details. [His brother, Jon, was to be his best man.]
A Boston University spokeswoman told Boston radio station WBZ-AM that Markoff had been suspended from the medical school after his arrest.
Neighbors told WBZ correspondent Christina Hager they were stunned at the news of Markoff being charged with murder.
Michael Bernard, who lives in Markoff's building in Quincy (left), was shocked to recognize his neighbor on TV reports of the killing.
"He was smart, he carried himself well, he was clean, a good looking guy," said Bernard, a retired electric company worker. "He seemed like the type that would have it all. It doesn't make sense."