Life for a Life ?

[WMD351]

The young guy who kills the old pervert who fiddled with him when he was a kid?
The battered wife who was beaten to a bloody pulp and abused every day of her life for decades before she snapped and killed her partner?
I'm of course not saying that they did the right thing, but what are their chances of reoffending (I have no idea myself) and what benefit comes from giving them life or putting them to death?
I've got no source for it, but I've heard many times that murderers are known by their victims well over 50% of the time (quick search suggests the % is from 60 - 80% but has no evidence or proof).
How many people in jail for murder are people who never committed a previous crime in their life, maybe never would again, but at one point in time they made a mistake?

Now naturally I'm not suggesting that these people can in any way be compared to a paid hit man or recidavist violent offender with a life long criminal record, but this issue is a long way away from having a black and white yes/no answer, in my opinion anyway.