. >> with sabrina zunich now booked and in the lockup, detective ron parmertor began the investigations wasn't a case in which you had to wonder who was responsible. >> that's correct. we knew right away it was the foster daughter. >> this looked like a case that could be shut as quickly as it opened, but if that were true, we wouldn't be telling you this story. this turned out to be one of the most unusual cases we've ever come across. police would end up investigating not just who but why with answers as stunning as they were disturbing. as dawn broke that cold november morning, detective parmertor began with his perpetrator, sabrina zunich. >> i first noticed that she was a very small girl, very frail girl. >> sabrina started describing the moments leading up to the murder. she'd had a migraine she said. while everyone else slept, she walked into the knoefels' master bath to get some ibuprofen, and that she said is where her memory went blank. you didn't think anybody could stab somebody that many times and not remember any part of it? >> no. i mean, i tried all different ways to ge