>> three months later, they found the electrical box. three months after the bombing the fbi dive team found the electrical box in which the bomb had been placed. but after months of sitting in water and mud there was no trace of dna or fingerprints. the only story this peeled metal told was -- this case is going nowhere. >> reporter: now with little hope of finding the key piece of evidence that would put the case away, the detectives tried that good old fashioned tool of policing, shoe leather and tire tread. around-the-clock surveillance of peter and paul moore. aided by tracking devices with a particularly helpful app. >> they're called geo fences. i put a geo fence around where i live, i put a geo fence around the sheriff's department. >> reporter: protection he felt he needed after someone targeted law enforcement with those spikes on the road. >> if the vehicle or the gps monitor travels into those locations you get an alert.