Lois Riess' son says he's stunned she's been accused of killing two people — including his father — and claims she was a "good lady."

"It's unbelievable," Braden Riess, 30, told Inside Edition in an exclusive interview that will air in full Thursday. "I can't wrap my head around it. My mom was a good lady."

Riess, a grandmother, is accused of killing her husband, David, in Minnesota in March before heading to Florida, where she befriended a woman who looked like her. She then allegedly killed the woman, 59-year-old Pamela Hutchinson, and stole her identity.

Authorities eventually caught up with Riess — who published reports dubbed the "killer grandma" — in Texas and extradited her back to Florida, where she remains.

Braden, her youngest son, said she'd struggled with a gambling addiction before her alleged crimes.

"She had her own demons, you know, lately," he said. "Something happened in her brain that made her snap."

For more on the interview, tune into Inside Edition Thursday. For local listings, click here.

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