they may not have seen any inherent dangers," O'Toole said.

The last night she was seen alive, Costello had two lengthy conversations with a man who answered her Craigslist Long Island ad, said her roommate, David Schaller. She agreed to meet him in a car parked around the corner, Schaller said. The client would pay $450 for two hours or $1,500 if she spent the night with him.

But the man set conditions: She was to bring nothing and tell no one where she went.

Schaller told her not to go.

"You can't do this," he said he told her. "At least take a phone so you can call me if something happens."

Costello refused, he said. "That's not what he wants," Schaller remembers her saying. "She said it was big money."

It's unclearwhy, but "something made her trust him," recalled Schaller, who said his cellphone was used for the conversation and that he overheard parts of it. "It was like she knew him."

Abandoning their own rules

Crystal DeBoise, co-director of the nonprofit Sex Workers Project in Manhattan, said most prostitutes -- from street walkers to high-end call girls -- develop safety rules. Many work only in hotels, others inform friends and pimps of their whereabouts and some even ask clients for references.

"Are there people who can't follow safety precautions all of the time? Yes, just like any industry, sometimes those rules are abandoned," DeBoise said.

Brainard-Barnes' sister still wonders how she ended up on Long Island. "My sister said she would never go outside the five boroughs," said Melissa Cann, 27, of