BOSTON, April 18, 2009 -- Three crimes.
One man police the FBI wants to talk to.
Captured on a series of surveillance cameras in Boston's upscale Back Bay, the 20-something, clean-cut blond man was seen leaving a luxury hotel where police said, 26-year-old masseuse Julissa Brisman 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 massage or erotic services on the Internet classified site Craigslist.
The first crime happened Friday, April 10, at the Copley Square Westin hotel in Boston. Police say a woman, who had advertised exotic services on Craigslist, was held at gunpoint, bound and robbed of $800.
Then, on Tuesday night, April 14, Brisman was killed at the Marriott, just next door.
Finally, late Thursday night -- an hour south in Rhode Island -- there was another similar attempted robbery.
Police said all the women were tied up and threatened at gunpoint. It is believed that Brisman may have tried to resist her attacker as he tried to bind her wrists, and was shot.
Boston police are working with police in Rhode Island to determine if the cases are connected. There is surveillance video of the Rhode Island man who is believed to have attacked there, but that video is not being released at the request of Boston police.
A common thread among all of the victims is that they all had posted Craigslist advertisements for some sort of massage or exotic dance. Investigators say that's a vulnerable venue to offer personal services.
Former FBI agent and ABC News law enforcement expert Brad Garrett said Craigslist is a first choice for many looking for sexual services.
"By some sources, it's one of the leading avenues to promote prostitution because it's so easy," he said. "You place an ad, you say, 'Come to Hotel X, at a time and date' and a service is provided. It's really an ideal environment for criminals."
Earlier this year, New York radio anchor George Weber was murdered in his Brooklyn apartment, and police said they believe the killer answered Weber's Craigslist advertisement offering $60 for "rough sex." Weber was stabbed more than 50 times.
Gay Talese, an author who writes on the sex trade whose most popular book, "Thy Neighbor's Wife" came out long before sites like Craigslist, said such sites are making the problem much bigger because the players are anonymous.
"It's instant communication, it's instant sex, it's sometimes instantaneously a tragic situation," Talese said. "The reason it's definitely bigger is because any sense of caution or guilt associated with sexual interchange of a commercial nature is eliminated now."
Just last November, Craigslist entered into an agreement with 40 state attorneys general to eliminate some of the anonymity by requiring credit cards to post these erotic ads.
The company CEO told ABC News the are deeply saddened by the events and are "evaluating the incident to see if they can better protect Craigslist users."
But experts say little can be done to prevent criminals from using the Internet to stalk their prey.