There is no legitimate cause for murder. If you’re found guilty, it wasn’t something like self-defense.
The only thing you can do with people like that is mitigate the risk they pose to others.
Your judicial system has determined that the risk has been mitigated. I’m not sure if I’d agree with the overall assessment, but I would bet that gainful employment helps with the mitigation.
Some places treat rape as a mild crime. If you’re in the US, which you might be, I’ve always found that weird… anything sexual is incredibly taboo, but the punishments for rape in some places are so “toned down”, like punishments for neglectful killings involving vehicles. It’s like they tone the punishments down because they don’t think they’re that bad.