The mother of the alleged victims, who were 9 and 8 when Powell allegedly filmed them in various stages of undress, testified she learned about the allegedly peeping tom from an investigator who showed up at the family's home, The Salt Lake Tribune reported.
"He explained to us that when we lived at our rental house, our neighbor had taken pictures of us," the mother said.
She answered "absolutely not" when asked by Assistant Pierce County Prosecutor Bryce Nelson whether she had ever given anyone permission to film her children inside the family's home. She confirmed photos shown in court were of her children in the home's bathroom.
The older girl, now 15, testified she and her sister would use the bathroom with the door open because they were afraid to take a bath alone.
On cross examination by defense attorney Mark Quigley, the mother said she had seen another member of the Powell household, with dark hair and a beard, wearing pajamas and a robe, outside occasionally.
Powell, father-in-law of missing Utah woman Susan Powell, kept his voyeurism secret for years, Nelson said during his opening statement earlier in the day. Nelson told jurors the investigation into Susan Powell's disappearance uncovered Powell's activities, the Tribune said.
Detectives searching his files for information on his daughter-in-law found a computer disc, "disc 12," with images of a neighbor's two young daughters taken surreptitiously while they were undressing or using the bathroom in their home outside Puyallup, Wash.
Nelson said the girls and their parents were not aware of "a secret that Steve Powell kept hidden until Aug. 25, 2011."
"The evidence will show that the defendant filmed the girls for sexual gratification," Nelson said.
Steven Powell became notorious during the search for Susan Powell when he claimed she had come on to him sexually. One of his daughters came forward and said the opposite was true -- that her father had made overtures to Susan.
Quigley told jurors the case is not about Susan Powell or her deceased husband Josh. He said the prosecution still has the burden of proof in the case.
Susan Powell vanished in December 2009 from her home in West Valley, Utah. Her husband said he returned from a short camping trip with their two young sons to find her missing.
Investigators have said they are convinced Susan is dead and named her husband as a person of interest, although he was never charged. Josh Powell killed himself and his sons in February in an explosion at his rented home in Puyallup.