about who the killer might be, and the more they talked, the more detectives wondered if perhaps shirlee sherman had actually been the intended target. >>> coming up -- a secret in the sherman familiar supply she hated him because of what he had been doing to me. >> and a think person of interest. >> immediately there's a buzz. could it be him? like, could it have been him? >> when "dateline" continues. ♪ >> reporter: as a building contractor brad waite spends a lot of time in his truck. >> reporter: he's haunted by the possibility that at the very moment his sister, shirlee sherman, was being murdered in march 2008, he was driving by, close enough, perhaps, to have heard her scream. >> i basically almost drove by hunter's house, and so it would have been at 4:00 that afternoon. i'd had no idea shirlee was working there that day. >> reporter: later that night, brad says he heard about the two murders in dundee on the 10:00 news. even then he says he didn't know his sister was a victim. that news came later, in a phone call from his brother, dan. >> danny called me. it was at 11 -- at 11:30 that