Mr. Blair Garrow is what we might call a piece of work. His aw-shucks, neighborly attitude goes right out the window when Georgie and Billy discover his counterfeiting business. He comes after them with Bowler Hat, and while Bowler Hat is clearly the hired gun in this operation, Mr. Garrow is the brains, and he's willing to kill to keep it a secret. This is a guy who dumped his own daughter's body on the side of the road to keep from having to tell his wife she died in an accident. Mrs. Garrow says, "I'm the one thing he is afraid of" (24.39), but we're not so sure.
Though it turns out he doesn't have anything to do with Agatha's death, we're glad he ends up in jail all the same.