Well, except for keeping violent repeated offenders behind bars instead of releasing them a dozen times, as it happened with this idiot. Doubt anyone would be opposed to that but somehow, he was allowed to still be out there.
That'd be one of the ways to prevent potential additional crimes and sprees like this.
As for him getting out, even shooting at a single officer is enough to get you some years. Hitting 6? No way this guy won't ever get out now no matter what.