Who is Older Frank from Somewhere in the Darkness and what is their importance?

Frank is an old running buddy of Crab's. Frank is a part of the armored car robbery. Crab suspects that Frank shot the guard because Frank tells the police that Crab was with him and that Crab shot the guard. Crab thinks that Frank pointed a finger at Crab to protect himself. Frank got only a few months in jail for the robbery and is now dead, which is why Crab decides to go to Rydell for the truth.