DIAMOND, Mo. (AP) -- No one will ever confuse Jim Murray with a teenager. His tall frame, broad shoulders and clipped gray hair give him away for the grandfather he is.

But for a 69-year-old retired small-town police chief, Murray cuts a credible figure as a 13-year-old girl surfing the Web, looking for friends. He knows all the instant-messaging shorthand, the emoticons, the places to find men looking for sex with children.

Murray's retirement job from a rural home office has netted 20 arrests since he started in 2002, but his latest catch was the first elected official: four felony enticement charges against a small-town Missouri mayor, who after his arrest called Murray up and begged him to make the case go away.

Nineteen other defendants have included a Missouri furniture company executive, an Arkansas professor and a Tulsa, Okla., school security guard. Ten of those men have been convicted and sent to prison. One was deported. The other cases are still pending.

The defendants ranged in age from 24 to 62, with an average age of 39.4 years, and mainly come from Missouri, Arkansas and Oklahoma, Diamond police said.

Internet child safety experts say cops like Murray are heroes who do good work at the cost of wading through the muck of online pedophile fantasies.

"He's a trailblazer. 2002 was very early for smaller police departments to start doing this," said Parry Aftab, executive director of Wiredsafety.org, a children's Internet safety group.

"This is an ugly part of the world. You may be talking online to someone who thinks you're a parent willing to trade their 3-year-old child for sex," Aftab said. "It's a part of the world that no one wants to be exposed to."

Murray, who taught elementary school for 27 years before switching to police work, is more humble.

"This is really about the kids," he said.

The first thing he hands a reporter at the start of an interview is a neat packet of newspaper stories about Kacie Woody, a 13-year-old girl in neighboring Arkansas who was abducted, raped and killed by a man she met online. It's not a case Murray worked on. Instead, he said, it's "a motivator."

"If they want a 13-year-old girl, I want to be that girl," he said. "If we don't stop these guys, they will hurt a real girl."

Murray said he manages to shake the online conversations out of his head after a while, but they can still make him angry.

"There'll be times when you just want to reach through the screen and choke them or slap them. To think they could talk that way to a girl."

"I want to catch them," he says, his voice turning quiet. "I want them to pay."

The latest defendant is Allen Kauffman, 63, who resigned as mayor of Collins and pastor of Temple Lot Church after he was arrested Jan. 11 at home in his small Missouri town about 110 miles southeast of Kansas City.

The probable cause statement for the charges is full of the shorthand, rapid-fire messages that make up online chat. They give a sense of the lurid, grimy exchanges that can develop between a child and a stranger online.

Murray was logged into a Yahoo! chat room as a 13-year-old girl named "cindyndiamond" using the screen name "Cin" when he was first contacted Nov. 15 by "duke dukeadk", who prosecutors allege was Kauffman.

Duke contacted Cindy again the next day and said he was 55. The exchange included:

Cin: i like to french kiss...senior boy taught me.

duke dukeadk: but it depends on where you want to be kissed at lol.

Five minutes later Duke asked:

duke dukeadk: so you a virgin

In at least five instant-message sessions through mid-December, Duke went on to tell Cindy he wanted to have sex with her, to ask for nude photos of her and to suggest Cindy have sex with another girl in front of a Webcam so that Duke could watch.

In a Dec. 1 message, Cindy said they lived far apart and Duke responded:

duke dukeadk: it would be worth the drive if i got to make love to you

Duke did not propose an actual meeting in any of the exchanges listed in the charging documents.

Murray has arrested other men arriving for trysts they believed they were setting up with the detective's teenage persona.

Murray was chief of police in the farm town of Diamond from 1995 to 2000, when he retired. After getting a home computer around 2000, he discovered chat rooms and was angered when he was offered pictures of young girls. From there, he developed an interest in Internet sting operations.

Murray contacted experts in the field, including Sunny Parmer with the Royal Canadian Mounted Police, and got training from the National White Collar Crime Center on basic computer data recovery.

Now he patrols the Web from a cramped home office divided between his police computer and a personal computer ringed with photos of his six grandchildren and three adult kids.

Murray remains a detective on reserve status with the Diamond police, but he donates his investigation time. He says he only spends about 30 minutes a week on average in chats but several hours more going over hard drives of arrested suspects looking for contacts with other potential victims.

"Fourteen years working with Diamond PD, I never had anyone come up to me and say I'm really glad you gave me a speeding ticket. But several people have stopped me at Wal-Mart and the filling station and said they appreciate what we're doing on the Internet stuff. And that's a good feeling."