What happens when you injure or kill someone in self defense?

If the DA decides there is evidence that you didn't act in self defense he prosecutes. If a jury of your peers agrees you get convicted. If they find you not guilty you can't be retried on the same charges.

" Could they come back years later and decide to prosecute you?"

Yes, this is possible. If the DA decides not to prosecute he generally doesn't change his mind unless evidence emerges that you didn't act in self-defense.

"Assuming it was justified do you get documentation stating this?"

Generally, no. But the police investigation is a matter of public record. Any charges against you must be supported with evidence. You don't have to prove that you're not guilty. If they don't charge you, your legal status is no different than if it never happened in the first place. Anybody can be charge with a crime if evidence exists that they acted illegally.

Murder is a crime, and faces penalty. A person who murders another will likely be charged. That person will need to go on trial as a defendent against the State. The State needs to convince the Jury the murder was malicious, the Defendant needs to prove the murder was in self defense.

The jury makes the decision.

The same is for an injury.

The nature of the case plays a big role in the outcome. The Zimmerman case for example, is a good one to reference.

I'm speaking from the English Law (it may be good to check because you're American)

The law opperates from the laws of the time- for example; if I murdered someone on the 1st Janurary 1990 but a law that made murder illegal on the 2nd January 1990 then I would get away.

If you did kill or injure in self defense and have proof then you should be good :) Hope this helps

nothing happens, thats why it's called self defense.

You wouldn't go to prison.