Drew Peterson's son is the last witness in the Drew Peterson trial as the defense rests.
The son of a former Bolingbrook police officer accused of killing his third wife said he's never suspected his father had a role in her death.
"He was very, very shaken up about it. I'd never seen anyone so sad in my life," Tom Peterson told jurors Wednesday. "It was very troubling to see him so shaken up."
Peterson's father, Drew Peterson, is fighting first-degree murder charges he killed Kathleen Savio in an effort to protect his financial assets following their divorce.
The 19-year-old, a neuroscience student at the University of Pennsylvania and the valedictorian of his Bolingbrook High School class, assured jurors his testimony was "completely voluntarily."
Dressed in a suit, the young man spoke politely about his father, his mother and his step-mother, Stacy Peterson, who disappeared in October 2007.
"We all had a really good time. Stacy was very fun," he said.
Tom Peterson was 11 years old when his mother was found dead in the bathtub of her home.
"She definitely liked to have hot baths," he recalled, adding that as a young boy he and his younger brother used to share baths with their mother.
He recalled how Savio would sometimes pull her hair up if she intended to bathe without washing her hair. Other times she's leave it down and then be seen with a towel wrapped around her head.
During cross-examination, prosecutors reminded him of his 2008 grand jury testimony when he said he didn't know much about his mother's bathing habits.
Asked if Savio ever took baths in the morning hours, he said it sounded "highly unlikely," but said he "wouldn't know that either."
Peterson last year withdrew himself from the wrongful death suit filed on his behalf by his aunt and grandfather. His younger brother, Kristopher Peterson, followed suit when he turned 18 years old earlier this month.