ST. CHARLES COUNTY, Mo. — From the twisted world of killer Pam Hupp to the salacious porn camera case involving a convicted police officer, there’s one detective who made sure neither suspect escaped.

“My job is not to be on camera and not to be seen or heard because my job was to back up the frontline investigators,” said detective Larry McClain.

McClain is a digital forensic investigator and an adjunct professor at Lindenwood University. He teaches cybercrimes.

You can see him at the 2016 arrest of Pam Hupp, wearing plain clothes and rubber gloves. He was grabbing Hupp’s cell phone.

“Of course, that phone, the same phone she had in her hand when she called 911,” said McClain.

Now proven to be a fake 911 call and a scene staged by Pam Hupp, Hupp had claimed someone invaded her home and that she was forced to shoot.

“So in my mind, she is just a victim, and we treated her absolutely as a victim of a crime – until we knew different,” he said.

McClain used seven search warrants to track Hupp’s digital footprints.

“It really is like DNA,” he said. “I would argue even better. It’s a third-party independent witness. It doesn’t have skin in the game.”

Hupp had claimed a man with disabilities came out of nowhere to attack her at her O’Fallon, Missouri home. But McClain found Hupp’s digital footprints 17 miles away, right at the supposed attacker’s front door.

“I remember sitting there a minute,” McClain said. “It was an interesting moment for me, and going, ‘She did this!’ And I knew, and I knew no one else on the planet knew for that brief shining moment.”

The case was not complete without incredible discoveries by dozens of other officers, but the cyber investigation remains key, as it did in another previous FOX 2 exclusive. In 2014, we found now-former officer David Cerna operating a hidden porn camera in a public restroom.

McClain was the detective who followed up after we notified the police of what we’d found.

“And I was following you up, which you didn’t know, to make sure that I had a match,” he said. “And then I was finding all those bathroom videos.”

Then, we began finding more videos. I certainly found the video that you mentioned in previous reporting, where he was filming inside the pants of a juvenile on traffic stops, and a video that was produced at his house.”

Former officer Cerna has been in and out of prison and currently faces new sex offender charges. Pam Hupp is serving life in prison for murder and currently faces another charge for the 2011 Betsy Faria murder.