So is the problem that we are not killing these guys? Or that they are not serving life behind bars? Like I said, death is only warrented (in my opinion) if another life is at risk.
Even the ones serving life sentences manage to kill fellow prisoners and guards regularly. Not to mention having other people killed outside the prison, as Allen did. "Tookie" Williams came very close to killing fellow inmates more than once. Allowing known stone killers to continue to live puts everyone within their reach at risk.
Right now, there is a woman running for the Democrat gubernatorial primary whose claim to fame was her Tookie advocacy. If she had been Governor, that monster would be on the streets.
A judge cannot release a killer back into society if they have been executed.