The two main characters in the story are the two men who used to be such good friends -- Jimmy Wells and Bob (whose last name we do not know). I think you could argue for each of these men being the major character. I will say that I think Jimmy is truly the major character because the story turns on what he actually does in the story(whereas Bob is only important for what he has already done before the story).
Bob has become a criminal so in that way he is bad. On the other hand, he remains good enough of a person to remember Jimmy fondly and want to keep their meeting.
I agree with the previous editor, bu if I were to chose one character over another I would say that Bob is the main character. The focus in the story appears to center around his visit and recollection of his last meeting with his friend Jimmy.
Through Bob's telling of the tale of how he had met with his friend years before and they had set a date to return and discuss how their life turned out, the reader is drawn into the story. For most of the story the policeman only presents as a secondary character. The reader does not know his importance until it is revealed at the end of the story.
i think jimmy wells is the main character because story revolves around him as he comes to meet bob