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This was Stacey DeLuca's plan: Chat online with child predators while pretending to be a young girl. Just a few hours.

"I'd rather have them talk to me than a real 13-year-old," the 21-year-old said.

It didn't take long before a 50-year-old California man allegedly told DeLuca — who was posing as 13-year-old "Jess" from Massachusetts — that he likes "younger girls" and that she wouldn't be his first.

DeLuca called police, and stayed in character for a month, saving transcripts of the man's lurid comments and graphic photos from the Yahoo Inc. (YHOO) chat room.

The result: Lawrence I. Katz of Oceanside, in San Diego County, was charged with attempting to send harmful matter to a minor via electronic means. He's fighting the charges.

"I was totally surprised," said DeLuca, a Worcester resident who works in the promotions department of a local radio station. "You get in a chat room and you get tons and tons of instant messages. These guys wait to talk to some little girl."

DeLuca is among a growing number of civilians across the nation who are conducting online stings to catch potential child predators. Perverted Justice, an organization that's dedicated to outing online predators, expects to double its volunteer corps, to 100, by year's end.

Critics say it borders on vigilantism. Criminal defense attorneys argue that it amounts to entrapment and that the nature of the charges — rather than the weight of evidence — forces people to plead guilty to avoid publicity.

Law enforcement officials warn that sloppy civilian investigations will push predators further underground, and that civilians may be endangering their own safety.

"In criminal justice matters, control is key," said Gerry Leone, a former state and federal prosecutor in Massachusetts. "Civilians who haven't been trained lose the aspect of control."

NBC's "Dateline" program has helped popularize the practice by teaming with Perverted Justice to lure adult men to a "meet."

The men expect to find a young sex partner, but are instead met by TV cameras, and more recently, by police officers as well.

In the program's fourth sting, 17 men were arrested in late March when they traveled to a home in Greenville, Ohio, where they expected to meet an underage girl, according to the Darke County Sheriff's office.

Perverted Justice, which was paid by NBC to run its latest sting, boasts of having contributed to more than 50 convictions nationwide, all detailed on its Web site.

The group, based in Portland, Ore., enlists volunteers to go undercover online.

It has inspired a rival organization, called Corrupted Justice, which decries Perverted Justice's practices as vigilantism. Corrupted Justice says investigations should be conducted only by law enforcement.

The Justice Department says stopping online predators is a top priority. Total federal prosecutions of child pornography and abuse cases increased nearly fivefold from 344 in fiscal 1995 to 1,576 in fiscal 2005, a top Justice attorney told a congressional panel in April.

And the federally funded Internet Crimes Against Children task forces' investigations resulted in 3,423 state charges and 563 federal charges in the first half of 2005, according to DOJ attorney William Mercer's testimony.

Sgt. Jeff Skuza, head of investigations for the Fargo, N.D., police department, said civilians can be helpful, especially because many departments have limited manpower.

Working with a Perverted Justice volunteer in March, Fargo police arrested four men who showed up to a meet.

"We're happy with the integrity" of the evidence, Skuza said.

Civilians inadvertently can damage a case, some police say, by scaring off the target. A Massachusetts man burned the hard drive of his computer in his fireplace before police searched his home two years ago after Perverted Justice publicized the man's solicitation of a minor. He wasn't charged.

DeLuca rejects the notion that she's taking the law into her own hands.

"I'm just sitting in a chat room. They're the ones contacting me. I'm not starting any of the sex talk," she said.

DeLuca, who is engaged and has no children, visited the Perverted Justice Web site after watching a recent "Dateline" special. She learned how to be a chat room monitor, created a fake Yahoo profile using a photo of a child actress, and a day later was contacted by "Paul Robinson," who allegedly turned out to be Katz.

"There was one night a week when his wife wasn't home, and he'd stay on for hours," said DeLuca. "We'd talk until he had to leave to pick her up."

Each day, she forwarded transcripts to police.

DeLuca, with police guidance, eventually set up a meeting. But before they could get together, another chat room monitor who was running a similar sting from Maryland revealed her identity to him, and he was scared off, DeLuca said.

Nevertheless, the transcripts and Webcam images allegedly depicting Katz involved in sexual acts while alone were enough to persuade San Diego County authorities to charge him.

Katz, a casino dealer, did not respond to calls seeking comment. His lawyer, Ivan Schwartz, declined to comment. Katz is free on bail, and a status hearing is scheduled May 12.

DeLuca used another fake screen name to pose as a 12-year-old in a sting that led to the April 2 arrest of Cory A. Renwick, 25, of Boston, who police said is a registered sex offender in Florida and Massachusetts, stemming from a 1998 Florida conviction on possession of child pornography.

Renwick pleaded not guilty to enticement of a child after he allegedly arranged a meeting with DeLuca.

Renwick has no phone listing in Boston. His lawyer, Patrick Sheehan, would only say: "He feels he's innocent. He looks forward to having it tried in court."

Cathy Green, a defense attorney based in Manchester, N.H., said many of the men she has defended in these types of cases were innocent.

Green said the sexual chats are "completely repulsive," but not criminal.

"The real question is, are you dealing with a child predator or are you dealing with someone engaged in a fantasy world who would never act on it," she said.

An advantage for police, she added, is that an "investigation" begun by a civilian rather than by law enforcement removes the entrapment defense.

DeLuca says she's partly motivated by a close acquaintance who was molested, but the perpetrator was never charged. She also says she's ready to testify if needed in the recent cases. Though she may take a break before her next sting, she doesn't plan to stop.

"No, I'll still do it, she said. "Who knows who these kids are that you're saving?"