shotgun. it belonged to seth's roommate who had just moved out. we showed lucas this photograph taken of seth at his home. if you look in the upper right-hand corner, lucas, the gun rack. >> yep. >> is your mosberg in that slack? >> yes, the middle one. >> lucas talked to deputies about the gun on the day of the murder. >> i told them it should be there. >> reporter: it wasn't there when crime scene techs scoured the trailer. and cops knew another place it wasn't. on the list of guns kept at the house that seth had written out for the dci agent. investigators felt certain the mosberg was used to kill lisa, but a big question remained -- >> where is it? that's what we want to know. where is the gun? >> that same sunday a team began searching the big, beautiful piece of property where seth and lisa were starting married life and preparing to raise a family.