we were swinging and missing regularly, on a dily basis. >> k.c. choi was willing to talk repeatedly without an attorney. >> free? k.c. you've been very cooperaive with us. >> the detective has my fingerprints. >> he says to you, i've seen this movie and now you've got to take my fingerprints. he's like a pro. he's seen it all. >> he's being very relaxed. i felt that she was very confident we weren't going to figure it out. >> what mr. choi apparently didn't know was that other officers were watching him 24/7. the surveillance teams noticed he was spending a lot of time at the public library and he was using the computers there. probably because police had taken away his phone and mirabel's computer, which was the one k.c. normally used. >> initially, we would have undercover policeman go into the library and walk around him and see what he's doing. at one point he's seen googling can a cell phone be tracked if it's turned off. >> that's certainly suspicious. >> it is. >> detective ramirez was consulting daily with orange county deputy district attorney

k.c. joy. >> his full name is cwang choi joy. >> weren't you out drinking the other night and had an argument> she started yelling at me. >> k.c. said it was just an argument. >> i don't like you, i'm not attracted to you. i said, maribel, we had a great time tonight? what's the problem? >> what was the problem? the detectives heard from her family something interesting. k.c. joy had wanted to be more than roommates with mirabel ramos. lucy told us the same thing. >> when did it become apparent to you that k.c. sort of had a crush on your sister. >> he called me and said, i'm like in love with your sister. >> i thought, oh, this is great. >> because you knew your sister wasn't in love with him. >> yes. it's a bad situation. at that point, i'm like, k.c., you're a good man and i'm sure you'll find somebody out there for you. >> but it's not going to be her. >> yeah. >> now, the woman k.c. told he wanted had told him not only did she not love him but he had to basically get out of her life. despite that, k.c. continued talking with police. >> mr. joy was being cooperative. >> he was. >> talking