Investigators say most sites cooperate with subpoenas, warrants and other requests for help. In particular, MySpace, owned by Rupert Murdoch's News Corp., has a former federal prosecutor as its head of security and maintains valuable logs on site activity for at least 90 days. Some sites maintain logs for much less time, if at all.
To listen to Cohen is to walk through dark corners of the Internet. There are gang members boasting on MySpace, killers revealing their obsessions on LiveJournal, teenagers sharing drug-making tips on YouTube.
Yet Cohen, in a cop's matter-of-fact manner, is measured in his approach. "It's like any community, communities we all live in. There are going to be criminals in it," he says.
Cohen began his career with the Indiana State Police like any other trooper, writing speeding tickets and responding to accidents. Eventually he moved into fraud and corruption cases, and found that his work increasingly included an online component.
At one session of his recent conference, Cohen's audience nods as he shows how officers can plumb public pages of social networking sites to get to know people before questioning them.
But his pupils have trouble accepting the particulars of Second Life, where people chat, shop, trade stuff and have sex -- and, in Cohen's estimation, launder money occasionally -- through animated characters known as avatars.
"Is this for people who don't want social contact?" one investigator asks.
Cohen shakes his head as if to say it's not that simple. "This," he says, "is our new world."