On the outside, Steven Powell looked like any other proud dad. With a camcorder constantly in hand, he recorded his kids’ important moments. He filmed graduations and weddings, family trips and even everyday activities.

However, it’s what he also filmed that sent him to prison and revealed to detectives investigating Susan’s disappearance that he was deeply obsessed with his daughter-in-law.

“He was a voyeur,” Detective Gary Sanders with the Pierce County Sheriff’s Office in Washington said to us as we sorted through evidence collected in a search of Steven’s home. “He just loved watching people. Women and stuff. Particularly Susan. He had that infatuation with her and he videotaped her when she was not knowing.”

Investigators knew something was off from the very beginning of their interaction with Steven Powell. Sanders told us the first time he interviewed Steven he was struck by where the conversation went.

“He starts talking about Susan and his electricity between them,” he said. “He just went off and not the normal ‘Oh yeah, my daughter-in-law went missing and I’m helping and I want to know where she is,’ and stuff like that. He went into his relationship with her. It went a totally different route.”

It would be years before police knew how deep his obsession really went.

After Susan disappeared, her husband, Josh, along with Steven, tried to sell the story that Susan was unstable, suicidal and likely ran off with another man. They both went on national TV, describing Susan as “flirtatious” and “sexual.”

Their proof, they said, was in Susan’s childhood journals, which Josh had taken with him when he moved into Steven’s house in Washington.

“That opened the door for us,” Sanders said, speaking of Josh and Steven’s plan to release Susan’s journal entries to the public. “Here they thought they were doing a great thing and publicly blasting Susan, but that gave us the piece that we needed. That gave us the search warrant that got us into the house.”

Police were able to collect those journals when they served that search warrant on Steven’s house looking for evidence in her disappearance.

They collected a lot more, too.

“There were 20-25 detectives there,” Sanders said, “and we all went, ‘Wow.'”

Locked inside filing cabinets in Steven’s bedroom, investigators found his stash of Susan’s things: her underwear, nail clippings, hygiene products and more. They found doctored photos of Susan and boxes and boxes of videotapes, labeled with things like “SP – Washing Face & Brushing Teeth” and “Susan on Stool – Pantyhose.”

For years, Steven took videos of Susan when she knew he was filming, and he took more when she didn’t. At family events, he repeatedly focused his lens on Susan’s body. He stalked her, hiding in parking lots and taking video of her through the windows of his van. He also took video of himself, watching his videos of Susan.

“He did a lot of looping where he’d play it over and over again, just for his own pleasure,” Sanders said.

It’s clear what may have started as a secret attraction turned into infatuation and eventually obsession. Through it all, Steven Powell tried to convince himself that she loved him back.

During our three-year investigation into the Susan Powell case files, we found one tape that could prove Steven’s allegations — that he and Susan were in love — were a lie.

A video tape that kept rolling after he thought he’d stopped it, Steven sat in his car with Susan and confessed his love for her. Her reaction says it all.

Subscribe to COLD to hear Susan’s response to her father-in-law and more.