estranged husband and her boyfriend checked out, police suspected a man named nick holbert had the answer. a convicted-sex offender. nick told detectives he drove kelli home from the bar that night but never touched her. to police, the story just didn't add up. and now, a total strange was ready to prove it. once again, here's andrea canning with "deep in the woods." >> reporter: autumn, 2012. kelli bordeaux had been missing for months. the searches continued, but were winding down. and so was hope. privately, many around town felt kelli would never be found. but in the forest, outside fayetteville, there was someone, still, secretly searching for her. no one knew. not police. not even kelli's family. his name was david marshburn. he didn't know kelli but had an intense interest in her case, from the day she disappeared. >> she was in the military. you just don't up and disappear.