mario's attorney kathleen zellner believes that what may have happened in this ladies' bathroom coulden. a stock boy, coming into this bathroom about a month after brian disappeared, saw that there was a leak in this bathroom and saw that it lead up to this panel. so, he stepped on this toiled lifted up this panel, and found a pair of men's underwear, size small. >> reporter: a size similar to rob, the underwear, handed over to the police. but kathleen says it wasn't entered into the evidence log and never made it to trial. >> that is a huge bombshell and that's why we want to have dna testing. we want to confirm if that was his underwear. because if that's got render's blood on it and carrick's blood on it, that is all you need to know about who committed the murder. >> reporter: so we don't know that for sure. you just need to check it out to see if that is part of the picture? >> yes. >> reporter: prosecutor combs admitted to 20/20 that the underwear was not tested but stated both the police report and the witness were available to mario's defense lawyer before trial. >> unfortunat