In January, Raymond Dooley of Port Huron, Mich., logged on to Yahoo! and began a fateful conversation with ''lil_rachel_mi,'' an underage girl.
A barrage of questions followed. Where was Rachel from? What did she like to do for fun? Was she a good girl?
She answered Dooley's questions, including one about her age -- 14 years old.
Then, the conversation took a different turn.
''You down to have some fun?'' the 23-year-old Dooley asked, according to a transcript. ''Come get you and bring you back to my place for the night maybe do some drinkin (sic) and just chill?''
A phone call and several flirty messages later, Dooley was on his way to meet ''Rachel.'' Instead, he got a big surprise -- not the police, but television cameras set up in a ''bust house'' by Perverted Justice, an Internet vigilante group based in Portland, Ore.
Within hours, Dooley's online handle, photograph and home phone number were posted on the Perverted Justice Web site. A flood of harassing phone calls from the site's contributors followed, until Dooley's father approached the Port Huron police to file a complaint against the tormentors.
Instead, police interviewed the younger Dooley, took his computer and downloaded the transcript of his conversations with ''Rachel'' from the Perverted Justice Web site.
In May, it took a jury three hours to convict Raymond Dooley of a felony sex crime.
''Justice was done and it was done correctly,'' Lt. Herbert Welser of the Port Huron police said.
For Perverted Justice, Dooley's case is only one of many the group is helping to prosecute these days. The site is run entirely by volunteers who lurk in regional chat rooms under fictional handles of underage children.
Initially, the site was a vehicle to embarrass, expose and harass would-be pedophiles as a deterrent to others. But with 25 arrests -- the majority pending in court -- and five convictions to its credit since the beginning of this year, Perverted Justice says many law enforcement agencies are turning to the group for help in dealing with a problem they don't have the manpower to address.
''I consider them a group trying to help us,'' Welser said. ''Our detectives just don't have the time to work these cases. We're a smaller police department and we're very happy there's an organization trying to help us in these cases.''
The site's founders and operators only identify themselves by pseudonyms on their Web site and in media reports out of fear of retaliation by the more than 500 alleged would-be pedophiles they've exposed on their site.
But when cooperating with law enforcement, they use their real names and information. When cases go to court, volunteers take their own time -- often traveling out of state -- to testify on behalf of the prosecution.
''We have people who worked in churches, we've had people in white-collar jobs, we've had people who are homeless and use the computers at the library to go and meet kids,'' said ''Xavier Von Erck,'' a Portland, Ore. man who founded www.perverted-justice.com. ''We're actually turning into a de facto agency that can build very good cases. It's very gratifying.''
One of the more notorious cases is that of Ryan Hogan, a firefighter with Engine Company 237 in Brooklyn who allegedly tried to lure someone he thought was a 14-year-old girl into having sex with him.
Hogan's arrest is the first Perverted Justice-related arrest in New York. The group hopes police agencies in New York will follow the lead of departments in other states and federal authorities. Smaller departments don't have the manpower to staff regional chat rooms with undercover investigators, leaving the job to state police and specialized units like the High Technology Crimes Bureau of the Westchester County District Attorney's Office.
Hogan was really chatting with a Perverted Justice volunteer, who worked with the Department of Justice and the FBI to arrest him. The Justice Department said Hogan allegedly masturbated on camera for the ''girl'' while wearing a shirt with the FDNY logo. He was arrested in May and his case is pending.
In chat transcripts, Hogan admits to being spooked by the possibility of a police bust. He allegedly tried to meet the girl anyway.
That, Von Erck said, is often the key.
''It puts a lot of fear in the pedophile community because we're not bound by a lot of the archaic, terrible court precedents about what a cop can do in that situation,'' he said.
Perverted Justice takes steps similar to what a police agency would take to protect the integrity of evidence taken during a ''bust.''
Site volunteers must log onto a proxy server when they enter a chat room. The system creates an archive of chat transcripts on a server in another state, and the volunteers don't have access to that server, Von Erck said. As a result, attorneys defending accused pedophiles can't charge in court that the transcripts were edited.
The evidence is uploaded to a file server accessible only by law enforcement. Included in the evidence is an MD5 hash, a digital ''fingerprint'' that computer forensic experts can match to an alleged predator's computer.
''In the same sense, if a house is broken into and a homeowner finds a pry bar outside and brings it in the house, we don't expect them to maintain an evidence log," Detective Mike Parks of the Fayetteville, Ark., police said. ''They can show us where they found it and we can document it in our reports.''
Parks worked with Perverted Justice in the arrest of Lowell Daniel Keller, a former employee with the Fayetteville school district. In March, Keller tried to meet a Perverted Justice volunteer who posed as a 13-year-old girl in Fayetteville. Around the same time, Keller had also been chatting -- and trying to meet -- with a 14-year-old girl who turned out to be a North Little Rock police detective.
Last month, Keller, 51 was convicted on both counts and faces a sentence of 5-15 years in prison.
Parks said the involvement of a Perverted Justice volunteer was ''a double-edged sword'' because it interrupted the original investigation into Keller by North Little Rock Police.
And, Parks said, collateral damage of the bust was Keller's family -- after Keller's photo, chat transcripts and home phone number appeared on the Perverted Justice Web site, visitors to the site called to harass him and often got his wife and kids on the phone instead.
''They didn't have anything to do with this,'' Parks said.
Now, with a program called Information First, Perverted Justice will embargo bust information from publication on its Web site so police can get the information -- and make the arrests -- without public knowledge. Forty-four police agencies -- from town and city departments to county sheriff's offices and state police -- participate in the program.
Like Welser, the Port Huron police lieutenant, Parks said there's no way his department could spare the manpower to safeguard local children adequately online. While he opposes some of the methods of Perverted Justice, he said he supports their work.
''This is a group of volunteers who are working to protect children on the net,'' he said, ''and I applaud them for that.''