>> he clearly stopped using. he was feeling healthier than he felt in years. >> reporter: but when detectives john o'brien and ty labbe learned about gavin's addiction, they had to consider a raft of new possibilities. >> he disappeared. maybe he overdosed we didn't exactly have any of those answers. >> driving all over the valley, we would have moments in the car of where we looked at each other and said, "i think this is a suicide. and then an hour later, we'd interview somebody and something would happen and we'd go, "i think this is a murder." and our feelings and our gut instincts are going different ways very early on very fast. >> yeah. it's got to be pretty unusual though >> it was very confusing >> reporter: confusing for lisa too. because here was another secret, the smiths were underwater on their mortgage on the verge of losing their home >> we were in a horrible position financially >> reporter: lisa discovered