yeah but no but yeah
"Maybe if he was in jail indefinitely a family in Idaho family would be alive"
Possibly - but leaving the moral/legal/justice aspects aside (!), whenever you lock people up you're incurring costs that mean you can't spend money elsewhere. I have no idea what the cost is in Idaho, but in Florida it's $20k a year and it's $28k a year in Washington State (it's on google, so it must be true).
So is it better to lock hundreds of people up on the offchance that they might do something, or to spend that money on investigating the crimes that have already happened? I suppose it depends how likely they are to commit a crime again. It's a dismal question from the dismal science...