A big part of the problem is jail space. The parole boards are always looking for candidates to release to make room for new prisoners. After they go through the lesser crimes, they start releasing the more serious ones.
The likelihood of the parolees commiting another crime is very high, and at that time the victim's family should sue the board.
I've never heard of that happening and there is likely a law preventing it,but a judge somewhere (probably Kalifornia) will someday rule that it can happen. A few mulit-million judgements and the practice will end. Same scenario with psychiatrsts that deem a criminal no longer a danger and recommend his release.
One of the State's primary responsibilities is the protect the citizens. Law enforcement should be funded before all else. If it takes incarcerating half the population to do it, so be it.
If we started executing murderers (routinely), the jail space issue would go away: 1) past murderers would not need cells, since they'd be dead, and 2) more people would be less inclined to murder.