>> do you think she had any idea what she was walking into? >> no. >> she was blindsided. >> on "20/20," the families of the two other girls right after sentencing tell their stories. >> i'm breaking inside. >> what really led their daughters to brutally stab their best friend 19 times? what signs were missed? >> there is nothing that when you look back makes you think, oh, why didn't i see that? >> plus, the chilling interrogation video. >> >> i might as well just say it. we were trying to till kill her. >> could you believe what you were hearing? >> i would never imagine my daughter was capable of hurting another person. >> david muir reporting. >> it was multiple stabbings with the intent to kill. >> the exclusive breaks tonight at 10:00, 9:00 central on abc. tral on abc. stopping for more pills right now. only aleve has the strength to stop tough pain for up to 12 hours with just one pill.