The Crossbow

A man is killed by a sniper with a crossbow. Gunn has a client with a criminal record, an upper-crust clientele sensitive to scandal, and a collection of weapons that used to include a crossbow. It was stolen and the client, Copeland (Henry Daniell), wants Gunn to find the killer before the police find Copeland. There are three more killings, including one at the house of a judge whose groundskeeper Karl (George Kennedy) controls a large unfriendly dog. Question: how did the killer get past the dog?