Why would the Prosecution do that? Wouldn't it have been perceived by some that they didn't think he was guilty and that they were backing down?
THe cost to Idaho is a valid factor. There were only two possible sentences for these crimes and he got 4 consecutive life sentences. Life without parole.
And he admitted he was guilty. He admits he did it - which, I think, is a very good outcome for the families. The verdict still gets read, it is now on record - he says he did it.
More killers should do this, IMO. For all we know, he has glimmers of conscience. He wants to spare his own family. I think some of the family members did not want to hear the details again at trial (this is based on interviews given some time ago).
The system itself is real and fair. It should be the case that guilty people can so state. To me, that's fair. Saying you didn't do something when you actually did, and then sitting and waiting for others to prove that you did it is to me, the opposite of fairness.
I do believe that at least one of the families did not want the DP nor did they want to continue their grief through the trial process.
IMO he threw himself on the mercy of the court and did so when he realized the new Judge was not brooking any nonsense and that the witnesses brought in today (Friday) were going to be damning.
Again, JMO.