There are extrenuous circumstances however, in the case presented, yes those circumstances are present. The capacity for the individuals in question to truly restrain the theif safely is almost nil. Yeu have NO clue how hard it is to hold someone down who is scared for their life. If yeu're comming at them with a sword, trust me, there is NO way that 3 people can hold them down and keep them steady unless all three of them are notably over the weight of the person they're trying to subdue, and even then it isn't always possible, and usually requires special training to do so.
There's not much reason to believe that the 4 who caught the theif could've reliably managed to detain him without excessive risk to themselves, and there's no reason to believe that they could've injured without killing.
People are idiots; permanent solution to temporary problem. Go commit suicide right now if yeu enjoy that line of reasoning, because it's the exact same thought process.
Human life should be valued. Hell, life in general should be valued. The funniest part though, is that the same people who are all for the DEATH PENALTY, are oddly enough, frequently the same people who tend to call themselves "pro-life". Seriously, WTH?
Keep in mind there's alot of reasons why people steal in the first place. There's even alot of cases where someone will go out and commit a theft the moment they're released from prison ON PURPOSE, because after blowing 20-25 years of their life in prison, they have no useful skills left, they no longer can work in the world, they have a criminal record, and in short, are now restricted to the only lifestyle they know anymore... and commit a crime just so that they can get back into the only place they're comfortable anymore, because they are no longer fit to live in 'the real world'. These are people who should be pitied, as they've not only had their lives ruined forever, often for a simple mistake or bad decision, but instead some would rather torture or kill them.
We're not barbarians, we're not animals, we just loooooooove to go on about how superior we are to animals... and then the same people who are most insistant that we are 'better' than a dog, are no better than one themselves; they can't rise above their basic instincts, and are little more than an animal that can use tools. They never truly learn to use their brain.
The next time yeu go out camping, I hope yeu get eaten by a bear that's defending its' home, because it's the exact same line of reasoning. Yeu have not even progressed beyond animal instinct.
Yeur home is yeur castle, and yeu have a right to defend it within reason, yeu do not, however, have a right to use lethal force inappropriately. Go ahead and check yeur laws on self defense... yeu're not even allowed to use a gun against someone who has a knife in most states.
Life is sacred, stop wasting it just because yeu feel yeurs is more valuable than everyone else's. If yeu have no value on life, or value property over life, yeu already are a criminal and just haven't committed a crime yet.
EDIT: after reading this over after posting, I realize I got a 'tiny' bit nuts in about the later half of this myself. After about the halfway mark, this wasn't really directed at anyone in particular anymore, just a generic rant and vent of frustration against people in general who have no value for life, and hypocrites. Of which I realize the whole bear eating thing was probably hypocritical as well, though honestly I don't really think I'd be pleased if it'd happen, though I do think the term 'poetic justice' would still apply.