and then -- then you have to sit back, scratch your head and say, "well, i wonder if both these guys did it?" and then if -- if you go with that theory, what is the motive? robbery? no. rape? no. i mean, how would you get these two people on the same page to kill this young girl? >> reporter: there was one other possibility -- did daniel frame nathan by planting that bag in his bathroom? after all, he lived in the same apartment. so, detectives went about the painstaking work of verifying every moment in the lives of those two young men on the day of the murder. and -- >> nathan was a hard, hard suspect. but after we do our timelines and we interview people, and we check his phone and we check surveillance videos and witnesses at class, he had an alibi.