Scenario: Man wearing a bulletproof vest with a rifle walks in, throws a tear gas canister and starts shooting at random. He pauses to reload, and someone pulls out his or her gun and places several shots in his vest, killing him.

What kind of sentence would this person get (the person who killed the shooter)? Manslaughter? If so, how long would the sentence be?

There is no way the man who killed the assailant would be charged with a crime, assuming the weapon was legally owned.

Edit: For the sake of completeness, let’s say that the person did not kill the shooter but injured him enough to stop his crusade. What kind of sentence would the person who injured the shooter get? And how long would it be (if there is any jail time)?

Self-defense is an affirmative defense to all murder and manslaughter charges, at both common law and every American statute I’m aware of. This means you’d need to prove you were acting out of a reasonable fear of death or serious bodily harm to yourself or others - but once you do that, you aren’t guilty of any crime at all. In a scenario like the Denver theater shooting, it wouldn’t be difficult to meet your burden of proof. It’s extremely unlikely charges would even be filed. Even if they were - unless the prosecutor were disputing these facts, defense counsel would almost certainly get the charges dismissed long before trial.

There’s a recent video of a 71 year-old-guy shooting the would-be robbers of an Internet café.
The police declined to charge him.

In the US, there is almost no chance that the person who shot the assailant would even be arrested. There is almost no detail you could add to the scenario that would change this, unless the gun turned out to be illegally carried, as** Ravenman** said.

Oh. I guess I must have been thinking too much of this case:

Had he not started shooting, but made it clear that he was a threat, then killing him or injuring him would both be justified, correct?

So beyond someone getting shot, what are the similarities?

Your scenario - a person starts shooting into a crowd, pauses to reload. A member of the crowd, with absolutely no reason to believe the shooter won’t continue shooting (since he’s reloading), shoots him.

Linked article - a store owner shoots an armed robber, who falls to the ground. Owner chases the other robber out of the store, comes back into the store, walks right past the first robber who is still on the ground, gets another gun, comes back to the first robber, and shoots him 5 more times.

The guy didn’t get convicted for his first shooting, at an active threat. He got convicted for the second shooting, at a robber who was no longer an active threat.

We’ve discussed that case here a few times before. The difference is that in this case, the pharmacy owner no longer had a reasonable fear of death or grievous injury when we went back to retrieve another gun, load it, point it at the unconscious robber, and fire it. That’s why he was convicted of murder. If he had stopped after eliminating the threat to his life, he would not have been charged.

I’m pretty sure that if someone had shot the Colorado guy before he fired a shot, that person who fired may have been arrested, but conviction would be unlikely.

That varies by state. Some states impose a duty to retreat.

i don’t think being in costume at a movie theater would be taken as a threat. all kinds of geeks and hyper fans do that for their cult favorites.

I think the fact you’re defending not only yourself but an entire theater full of people would negate the requirement to retreat.

True, plus being in a crowded theater would make a safe retreat impossible.

However, the OP hypothetical, while clearly based on the recent shooting, does not in fact state a location, number of victims, or any circumstances beyond the tactics of the shooter.

The fact that the hypothetical shooter is reloading, supposes multiple targets.

Or he’s just a terrible shot. Maybe’s he’s holding his gun sideways at waist level.

Correct. The basic rule is that when you act in defense of a third party, you “step into their shoes” and have the same rights of self-defense as they would in acting on their own behalf.

Unless a prosecutor could show that EVERY PERSON who was a potential victim of the mass shooter could safely retreat without endangering themselves, the the duty to retreat would be of no effect. And seeing how everyone was trying to get the hell out of that theater and many still got shot, there is no way that could be shown.

I have the feeling we are being set up for a slippery slope argument,