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The son of former Bolingbrook, Ill., Police Sergeant Drew Peterson now believes his father killed both his third and fourth wives.

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Steve Peterson made the admissions in interview for a Lifetime television special and to the Chicago Tribune.

“Do you think your dad killed Kathleen? Melissa Moore asked Steve Peterson for the Lifetime story. “I'd probably say so,” Peterson answered, adding, “I think this is the first time I've ever even said that, you know out loud that yeah, I think he probably did it.”

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“I've always known in my heart that Drew killed Stacy and Kathleen Savio,” said Cassandra Cales from the room in her suburban home that she has dedicated to her sister

Sitting in the "Stacy Peterson" room in her suburban home, Cassandra Cales talked about her sister and Steve Peterson's startling admissions on the Lifetime show 'Monster In My Family' in which he talked about his father's involvement in Savio's death, which Drew Peterson has always maintained was an accident.

“Honestly never gave it a second thought, it was anything but that. You first thought there was no way my dad would do that. No way and then over time, okay Stacy's not coming back and I finally came to the realization that maybe he did have something to do with this,” Peterson said.

Savio was killed in 2004, her death in a bathtub staged to look like an accident. Her case was reopened after Drew Peterson's fourth wife Stacy disappeared in 2007.  Peterson was charged and in 2012 convicted of Savio's murder.

Steve Peterson told the Chicago Tribune he now believes his father killed Stacy, too. Drew Peterson is serving a 38 year prison term for Savio's murder, but maintains his innocence.

"I would love some kind of closure for myself, for the kids, but it won't come from him, we know that,” Peterson said of his father.

“I'm not sure if Drew will ever admit to anything because he's got that sociopath narcissistic stuff going on,” Cales said, but she holds out hope that might change one day.

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