Who Killed Bob‪?‬

Bob is dead. He appears to have died in his study, alone and with the doors locked. On his desk are a pen and a photograph of his family - which are usually there.
What are not usually there, are the ice pick, claw hammer, kitchen knife and bottle of prussic acid which have been arranged on his desk. A lot of questions need to be answered. The main one is WHO KILLED BOB?