trapp seemed stuck. >> i think she got a little frustrated and got a little desperate and came up with the idea of using the computer database. >> reporter: that is, the computer database of sex offenders. if they had a serial killer on their hands, there was at least a chance he'd already run afoul of the law at some point. it was a bit like just poking a finger into the haystack, frankly, and hoping to encounter a needle. but worth a try. so trapp called this woman. >> all sex offenders on parole, they will have an anklet, gps monitor. >> trap asked lomeli were any of those gps monitors here where jarrae placed her last phone call or here, where she window up in a dumpster. >> and if you find the same guy at both locations, you're getting somewhere. >> mm-hmm. >> lomeli ran the search, and what were the chances? she got a hit in both locations.