Accardo was McGurn's driver, but he is not named by serious authorities on the subject as being directly involved.

Funnily enough the Massacre is not much of a mystery, though it remains officially unsolved. There is not much reason to doubt the Byron Bolton confession. Bill Helmer's book lays it out in (exhausting) detail.

Burke, Winkler, Bolton, Goetz, who knows who else, in all probability did it.

Burke was arrested with the guns, Bolton confessed, Winkler's widow confirmed. That's about as close to a closed case as you are likely to get .