Has it been explained why he is a hitman? It isn't realistic that a doctor would do that.
They have just had Patrick make references to the fact that he has changed since they went to med school together and "something" must have happened to him to make him change.
He's a hitman because Guza wanted to destroy his character. Period.
They have just had Patrick make references to the fact that he has changed since they went to med school together and "something" must have happened to him to make him change.