Do You Think Billy Was Killed Instantly?

With multiple windows, multiple doors, it is significant to the case that the delivery man when he gets to this wayside cafe is that he's able to walk right in. So it doesn't sound like this was locked as you would expect if they had shut the store down and the offender didn't take the time to walk up behind him after he shot the three victims. When you see that type of conclusion died instantly, it depends on the anatomy that the bullet passed through. Now the pathologist mentions copper sheath slugs with a central lead core. Is that significant at all or is that normal for the time period? Or is it normal now?