I don't get it

Recently, there’s a local serial murder case that has made the news.  The bodies of eleven women, mostly prostitutes and drug users, were found both in a man’s house and buried in his backyard.  He would lure them in with promises of drugs and/or money, then rape, murder and dismember their bodies.  Awfully gruesome stuff.

He, through his defense attorneys, had offered to plead guilty to all charges if the death penalty specification was dropped.  A number of the family members of the victims sent a letter to the county prosecutor asking that he accept this deal.  They wanted to be spared the emotional turmoil a prolonged trial would inflict upon them. 

The prosecutor declined.  He has made it clear he wants the death penalty.  Isn’t the point of our justice system that we punish the guilty not take revenge?  Since when is life in prison not punishment?  

The prosecutor is willing to put the family members through an extended period of anguish and pain, listening to what happened to their loved ones, for what purpose? 

What happens, if for some crazy reason, the jury finds him not guilty?  Don't say it can't happen.  Some people would tell you that it just did in Florida.

Not to be practical, but what about all the time and money spent on the trial?  Couldn't that be better used elsewhere? 

I don't understand the evil this man was able to inflict on so many people.  But what follows is just as confusing to me as well.

I just don't get it.