let's solve this. >>> after strangling a young prostitute to death, budding serial killer joel rifkinly event before killing again. >> maybe joel hadn't reached the compulsion to kill again hadn't reached a zenith to act out again. sometimes it's years or weeks. but for him it was 18 months. >> in late 1990 joel picks up julie blackbird under the manhattan bridge. his mother is again out of town, so they drive back to east meadow and julie spends the night. >> yeah, she slept some of that time, took a shower some of that time, watched tv. >> kind of like a relationship. >> hanging out, killing time. >> yeah, like friends. >> yeah. >> if you didn't know who you were listening to and what the outcome was, you would believe that they were a couple, you know, on a date. >> before driving her back to the city, joel agrees to go to an atm machine with withdraw extra money for julie. >> we were leaving and i hit her from behind once and then strangled her. >> why did you hit her? >> probably to stop her. >> but why, why did -- >> motivating? >> yeah, why? >> i'm not asking, you know, why did