Life in Prison with Parole after 20 years (which should be the maximum existing sentence IMO).
The guy is committed to killing people. I don't support the death penalty, but releasing him is just as insane as killing him in my view.
If he hasn't reformed after 20 years, then he won't be released. But every person, even the most supposedly "evil", can change, and should be given a fair chance to prove they have reformed.
Something this simple, where the system's preference is for parole but with an option to extend in extenuating circumstances rather than the other way around, would be a huge step in the right direction.