The Pierce County Sheriff's Office released about 3,000 pages of evidence in the case against Steven Powell, including entries from his journals that detail his out-of-control love for his daughter-in-law Susan Cox Powell.
“The fact is, I can hardly control myself when it comes to her,” Steven Powell wrote in his journal.
In passages from 17 spiral notebooks, which spanned more than a decade, Powell allegedly wrote of sexual fantasies and expressions of love for his daughter-in-law as early as January 2003.
He admitted he secretly recorded Susan and watched the videos while masturbating. In some entries, he admitted to "looking at her naked body under the bathroom door (using a mirror)."
The journals also included photographs of Susan and parts of her body. Powell confessed to secretly stealing her private belongings, like her underwear and the discarded papers she used to wax her legs, and even wrote songs about her.
"She is an amazing woman. I hope I am right, that she is in love with me, but of course there is the problem of her being married to my son," wrote Powell.
The journals reportedly indicated Powell believed Susan felt the same way, but when he told her about his feelings, she didn't speak to him for months.
When Susan Powell disappeared in December of 2009, Steven Powell called in sick to work for two days, according to police reports. Some suspect he was involved in her disappearance, but in his journal he claimed she ran off with another man and was certain he would see her again.
"I would be devastated were I to find out Susan was dead from any cause," he wrote.
Powell talked about being in despair at one point when he thought Susan was dead. He wrote he lost 20 pounds and said she was his reason for living.
Court documents released Tuesday also revealed that investigators in Utah almost immediately began classifying Susan Powell’s 2009 disappearance as a murder and kidnapping probe. It was largely focused on her husband, Josh Powell.
Last year, authorities got a warrant to search the Puyallup home of Steven Powell. Josh Powell and his sons were living there at the time. Investigators found explicit images of underage neighbor girls on the father’s computers during the search. He was convicted in May on 14 voyeurism counts and sentenced to 2 ½ years in prison.
During the trial, prosecutors described a 2004 diary entry in which Powell wrote "He is a voyeur and Susan's an exhibitionist and they're a perfect match."
Authorities said Steven Powell has been uncooperative in their investigation into the disappearance of his daughter-in-law, who he claims he had a flirtatious relationship with, something her family denies.
The two children were placed in the care of Susan’s parents, but Josh Powell was later allowed to see them. Police discovered hundreds of images of disturbing cartoon sex and graphic depictions of incest on Josh Powell's home computer, something Utah authorities investigating his wife's disappearance kept private for about two years.
In February, a Washington state psychologist altered her assessment after reviewing the images and ordered Josh Powell to undergo a psycho-sexual evaluation. That conclusion came just six days before Josh attacked the boys with a hatchet, then lit his Washington rental home ablaze, killing himself and his sons.
KING 5's Elisa Hahn, Liza Javier and Travis Pittman contributed to this report.