Steven Powell was convicted of 14 counts of voyeurism in Pierce County Wednesday.
The jury returned a unanimous guilty verdict on all counts, agreeing with prosecutors that photographs of girls and women in various states of undress found in Powell's possession last fall were used for sexual gratification.
Defense attorneys had argued there was too much reasonable doubt in the case to convict Powell.
Powell is the former father-in-law of Susan Powell, who has been missing since December 2009. Her husband, Josh Powell, who is also Steven's son, was a person of interest in her disappearance. He killed himself and the couple's two children in an explosion in Graham earlier this year.
During pre-trial motions, Culpepper ruled that images of Susan that were allegedly in Steven Powell's possession would not be admissible in the case.
The photographs prosecutors used as evidence were found at Powell's Puyallup home last fall when officers were searching for Susan's diaries.
Powell's daughter releases videos
Alina Powell put a number of home videos shot between 2007 and 2009 on a website: http://sites.google.com/site/westvalleymalfeasance/
The clips show her father, Steven Powell, playing with his grandsons, Charlie and Braden Powell, and sightseeing with his son Josh and his daughter-in-law Susan.
Alina wanted the public to see how Susan Powell did not seem to have any problem with her children spending time with their grandfather.