now back to "dateline." >> reporter: annie kasprzak had had a rough childhood. passed along from foster home to foster home before she was adopted by her case worker, veronica. annie's life finally seemed to be turning around. then in 2012, annie, just 15, was found murdered, her body floating in the jordan river. >> there was never a second that your mind didn't go to "this is not -- this is not what was supposed to happen." >> reporter: an eyewitness said she saw daniel ferry assault a girl the night annie was killed. that witness also said the girl had shown up with lj, whom police could never find. but in the course of their investigation of ferry, detectives learned something interesting. you had another lj in that crowd, didn't you? >> yeah. >> daniel ferry. >> yeah. >> what was his nickname? >> so he used two. one was joker, and the other one was lil joe. >> lil joe, lj? >> yeah. >> reporter: maybe their witness was confused or deliberately hiding the fact that ferry and lj were one and the same. either way, ferry seemed like their man. but the d.a. wanted