DEM
Law (Pretty Complicated?)
Their deaths are more unfortunate in the law's eyes than a petty charge on the man. You can't happen to kill someone in defense who wasn't going to kill you or someone else.
He might get a long year in jail and a relatively large fine for using arms to impersonate cruel and unusual punishment.
You only ask once if a life was in danger. If the man could plead that they were going to hurt someone, he'd be let off, though. I don't think you are allowed to shoot someone to keep them from running, but that's the issue. Supposedly, if you see them, the police will catch them. It's certainly not your fault if you don't shoot that they get away. Shooting implies lots of dangers as a civilian and amateur in arms. I think the police shoot them in the leg if they run.
If he wasn't sure, I think he'd be charged a fine and maybe less than half a year in jail, maybe even just a week or a day. If he just regrets ignorance, he might get a moderate charge.