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. sexual assault detective laura lomeli. >> all sex offenders on parole, they will have an anklet, a gps monitor. >> reporter: trapp asked lomeli, were any of those gps monitors here, where jarrae placed her last phone call, or here, where she wound up in a dumpster? and if you find the same guy at both locations, you're getting somewhere? >> uh-huh. >> reporter: lomeli ran the search and what were the chances she got a hit.