Judge Ronald Culpepper determined authorities had a proper search warrant when they scoured Steve Powell's home last year. In that search, they uncovered thousands of images of females being videotaped without their knowledge, including Susan Powell.
Steve Powell faces several voyeurism charges and one count of possession of child pornography. His trial is scheduled to start May 7.
Powell's attorneys had argued the warrant was illegal, saying it was essentially a fishing expedition designed to gather general evidence against his son Josh, who was Susan Powell's husband. Josh Powell was living with Steve Powell at the time.
Prosecutors said the warrant was necessary for investigators who were trying to solve Susan Powell's 2009 disappearance.
Culpepper determined there was probable cause to search the home and went even further to say there was "probable cause to believe that Joshua Powell, the subject of the investigation, was involved in the disappearance and very likely the death of Susan Powell."
He also said it was "very reasonable to infer that Josh and Steven would have discussed the disappearance."
Chuck Cox, Susan Powell's father, said it was a relief to actually hear those kinds of remarks in court. Utah investigators have never declared Josh Powell a suspect.
Cox also believes Steve Powell knows details of what happened to Susan Powell, and he hopes the trial will put pressure on him.
"Every step in this process reduces Steve's options," Cox said. "As those are reduced, hopefully it will motivate him to tell us where Susan really is."
While court documents indicate authorities were focusing on whether Josh Powell was involved in his wife's disappearance, investigators have said they also are interested in speaking with Steve Powell about his daughter-in-law's disappearance. They say he has been uncooperative in that investigation.
Alina Powell, Steve Powell's daughter, previously said she believes the evidence against her father was fabricated. She said Tuesday she doubted her father would get a fair trial.
Steve Powell's bedroom also contained images of nude female bodies with Susan Powell's face copied onto them, authorities said in court documents.
In one set of journals that investigators have described in court documents, Susan Powell wrote that she wished her husband would sever ties with Steve Powell. She described Steven Powell as a pedophile.