Why did a man take his own life?

Preview tonight's upcoming report.

by Chris Hansen, Dateline correspondent

As our "To Catch a Predator" investigation continues here in Murphy, Texas, we continue to see a trend that amazes me:  men who have heard about our investigations before --  and some who have actually watched them—still show up at our hidden camera house.

Take the case of 31-year old Eric Rubalcava. During the online chat, Rubalcava talked about how he wants to have sex with the girl and how he'll kiss her all over. When he showed up at the undercover house, he had camera equipment in his car and an excuse when he meets me. Rubalcava says he thought the girl was 18, but it's clear from the chat log the girl told him she was 13.

As the conversation continued, he recognized me and talked about seeing the "To Catch a Predator" series once before. I asked him what he thought about the show. He told me it was disturbing to see men go after young girls, but there he was allegedly doing the very same thing. The difference, he claimed, is that he really wouldn't have had sex with the girl, although he admitted that he might have taken some photographs of her. Like 23 of the other men who surfaced in the Murphy investigation, he's charged with online solicitation of a minor.

You'll also meet a man, alleged to have committed the same crime, who made a tragic choice. In two years and nine investigations, we've never experienced anything like this: Louis W. Conradt Jr. was an assistant district attorney in a neighboring county.  Before that, he was an elected district attorney. He'd been a prosecutor for more than 20 years and was well-known in law enforcement circles.  But evidence indicates that on this particular Saturday night, he was having a sexually-explicit chat and sending pornographic photos to a Perverted-Justice decoy posing as a teenage boy. Conradt also had a phone conversation with a decoy.

You'll see how we figured out the person on the other end of the chat is actually Conradt.

He never showed up at our house in Murphy, but in Texas you don't have to show up to be charged with a felony. The online solicitation is enough to get a warrant. And that's exactly what the Murphy police did.

Instead of facing the charges, Conradt chose to take his own life. It is a scenario that stunned everyone there. Precisely why Conradt chose to kill himself, we'll likely never know. We do know this: He didn't want anybody to see what he left behind on his home computer. Police say he put so many locks that local forensics investigators couldn't recover the information. The computers have now been sent to the manufacturer to defeat the locks.

I'll keep you posted.

'To Catch a Predator' airs tonight, Tuesday, 8 p.m. on NBC.