I’m told all the time let the police/gov’t agency/armed forces take care of a problem. When is it whithin our legal rights to take the law into our own hands? What are the limits to those rights? I.e. we see a person going to kill someone, do we call the police, try and stop the person, try and injure the person or even try and kill that person? Also how do the rights differ from country to country. I hope that this won’t lead to some sort of anarchy, but I think in our day and age it might be something worth knowing.
I believe that it’s acceptable to use reasonable force in preventing a crime being committed.
The interpretation of what constitutes reasonable is for the courts to decide, I suppose.
Well, that can be a pretty wide question. But in reference to your example, in most juristictions in the US, a person may use deadly force to prevent the death of another person.
This is definitely one of those ‘check your local and State laws’ situations.
But, generally speaking, if you saw someone, for example, stabbing another person, most juristictions would allow you to, as a further eaxmple, haul out your six-shooter and A) demand that the perp stop what he’s doing, B) detain him for the police, and C) shoot him if he continues his attack or attacks you.
But expect, no matter how “justified” the shooting, that you *will[i/] face charges. You may be aquitted, but you will very likely have to go to court to explain what happened.
What I usually recommend, is take an NRA self-defense class. Please, no knee-jerk reactions from the peanut gallery. The rules pertaining to self-defense are the same even if you don’t use, carry or even OWN a gun. The class will NOT “require” you to own a gun, and few instructors will try to convince you to get one if you don’t have or want one. They won’t try to recruit you as a member and they won’t slap a sticker on your car while you’re there.
The class focuses on the How, Where and Why of self defense. What’s considered self defense (running a guy over in a car isn’t, neither is shooting the guy after he’s down.) What conditions: Typically you can fight to protect life and limb, but some places won’t allow deadly force in defense of property. IE, you can’t cap a carjacker as he’s driving off.) When such defense is valid- If the guy’s running at you with a knife raised over his head, that’s one thing. If he’s fifty feet away and just yelling insults at you, that’s another. And even the level of force justified- Basically you shoot (if that’s your choice of weapon) to STOP, not kill Once the person has stopped attacking you, for whatever reason, you then have no justification for further application of force.
They also usually cover the old myths of self-defense, detailing things like why the old “drag 'em inside and put a kitchen knife in their hand” bit will land you in jail for a very long murder sentence, and other minutiae.
It’s terribly enlightening, and FAR better than asking some geek on the 'net about it. 
Cecil addressed the question of “citizen’s arrest” in one of his columns: Who’s the boss, city cops, state cops, or the Feds?
Some other points, all based on U.S. law:
You can (almost) never use deadly force to protect property only. Let them take it and call the cops. However, you may (depending on local law) be able to use deadly force to get a thief out of your house, even if he’s not trying to hurt anybody, on the theory that he could become dangerous. (And since he’s the lawbreaker, the law will generally favor you, not him.)
You can use deadly force to protect yourself from serious harm or death. You must honestly believe in the danger (called “ggod-faith belief”), but in many jurisdictions, you’ll be protected even if your belief is completely out of left field, or even if it’s based on racial prejudice. (Remember Bernie Goetz? I don’t think he did any time at all.) However, in practice, this often echoes a reasonability standard because even if you really did believe those nuns were paid Colombian assassins out to steal your kidneys, it’s tough to convince a jury that your wildly unreasonable belief was nonetheless in good faith.
You can also typically use deadly force to protect other from harm, but in this case your belief that the others are in danger must not only be in good faith, it must also actually be true. Therefore if you’re wrong, even if you have very good reasons to believe the third party is in danger, you’ll be guilty of a homicide. Again, this legal rule moderates somewhat in practice; if your reasons and your motives are really good, you’d get charged with something like negligent homicide with a very minimal sentence even though you’re probably technically liable for first-degree murder.
There are additional limits with these rules. For instance, there was traditionally a duty to retreat. If you were being menaced you used to have to try and run away and then, if that wasn’t possible, shoot only if necessary. Most states have abolished the duty to retreat, but some retain it. Also, aggressors can almost never use the self-defense privilege, although there are exceptions.
Rememeber however that every state has their own rules, so YMMV.
–Cliffy,
soon to be a lawyer (if I passed the Bar)
A somewhat easier way to look at it is like this.
Joe breaks into your house with a gun and you fight in the process the trigger is squeezed and he dies.
That is justified.
Joe breaks into your house with a gun you take if from him and knock him out cold. He is lying on the floor out cold. You, being really mad, point the gun and kill him.
This is NOT justified. You see once you cold konk him he is out cold and NOT a danger to you anymore.
How it would really play out in life is for the courts to decide.