Some initial thoughts:
Couples usually married in the bride's parish. Did his wife to be come from Southwark?
What leads you to believe that he named his son John Francis after the person who attempted to assassinate Queen Victoria? It is not an uncommon combination of names.

I may be wrong, but unless you have further information to indicate that he was a criminal, I think you are jumping to conclusions making the assumptions you have with the facts you have related here.
Did he give his address as the housing you mention in St Pancras?
Others may have more knowledge of how to locate records of convicted criminals, but the only things that come to mind are perhaps the Old Bailey records, or newspapers of the time.