Just because someon inflicts a crime on you in NO WAY free's you of guilt from doing another crime. Self defence is one thing, a guy running away is not a threat. Likewise if it were my family I'd be blocking the door, untieing my family, calling the police and an ambulance and getting them safe. Running down the street after one guy while my family are at home, defenseless and possibly in need of medical attention isn't protecting your family.
For those that think its fine, where does it stop, its ok to beat him in the street as he tried to run away, what if they caught up to him at his house, ok to take him prisoner and torture him for the location of the others, for minutes, hours, days, rob his house, kill him, what, where does it stop.
Ignore everything the burglar did, ignore his rights and simply look at what the guy did, he broke the law, if you, I or the burglar beat someone half to death in the street you'd expect to be locked up, almost killing a guy I'm not sure 30 months is even that long. Frankly I'd have given him a longer sentence and the burglar an even longer one. Obviously someone needs to make a call on his mental health but I'd still lock him up in some institution and get the other two in jail aswell. I'd also have locked up the other people who helped beat him to death as there was even less justification for them to do so.
The saving grace for the guy, who I do feel sorry for, is the burglar had such a thick skull, a bat to the head would have killed a lot of people let alone repeated other hits with bats, poles and probably punches and kicks. If he'd died he could, and should have done a very long jail term.
the law does not permit it at all. In fact it has a zero tolerance for what he did. 
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