You have to watch the movie in two parts to catch this. When the senator is killed in the beginning of the movie and again when Zavitz (bird watcher) is watching the video at home. When the senator is killed watch the guy that kills him and the dog. He walks around behind the dog to get to the senator. But when you watch the video at Zavitz's house just before he calls his friend at the paper the same guy that killed the senator doesn't walk around the dog but just walks to the guy. You have to pay attention because you may not see it right away.