Dan was the proprietor of a small retail grocery store.  One day while Dan was alone in the store, John, a stranger to Dan, entered the store, suddenly drew a revolver, pointed it at Dan, and ordered him to the rear of the store to open the safe.  Dan, believing John's revolver to be loader, made as if to obey.  After taking several paces,Dan whirled around suddenly, drew a revolver from under his coat, and fired twice in rapid succession at John. One of the bullets killed John, and the other, missing John, killed Xavier, a passerby who was walking along the street in front of the store.  In fact, Dan was carrying his revolver in violation of a state statute making it a misdemeanor for any person to carry a concealed weapon without a permit.  A subsequent examination of John's revolver revealed it was unloaded.  On the foregoing facts, Dan is separately indicted for the murder of John and the murder of Xavier.  Is Dan guilty of both of the crimes charged or of either of them?  Why or why not?  Explain your thought process.