"It's beyond comprehension to think a mother and daughter systematically poisoning their family members." Deborah Roberts' 20/20 prison interview with Diane Staudte airs Friday at 9/8c on 'Home Sweet Murder.' https://abcn.ws/3oPzNGJ | ABC 20/20

The mom who confessed to fatally poisoning her husband and son, in a new ABC News interview from prison, says she "can't tell" if she’s guilty. Diane Staudte spoke with Deborah Roberts for Friday's new 20/20, after pleading guilty in January 2016 to first-degree murder charges for her husband and son’s deaths and to assault charges for her daughter’s poisoning. Watch "Home Sweet Murder" - premiering Friday at 9/8c on ABC. Stream next day on Hulu. https://abcn.ws/3oPzNGJ | ABC 20/20