When Bart and Lisa enter the trailer and look at the binder on the desk, there is a pair of glasses on it. When the angle changes and Sideshow Bob is there, the glasses are gone.
Bart calls Sideshow Bob "an unstoppable killing machine"--but, as Bob later tells Edna, he's never successfully killed anyone.
Bob tells Lisa he has learned a thing or two about dynamite after being a homicidal maniac for ten years, but earlier in the episode Bob says it's been ten years since he and Cecil have seen each other, because of the incident where Bob got the job as Krusty's side kick, so that would mean Bob has been a homicidal maniac before he tried to kill Krusty, indicating a secret murderous life we've yet to see.