Missouri ? 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 the 69-year-old retired police chief of this small Missouri town 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.

Murray’s retirement job from a rural home office has netted 20 arrests since he started in 2002. His latest catch was the biggest: four felony enticement charges against a town 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.