It should, as with *ANY* penalty, be something-anything- that ensures 100% chance it will never be repeated. IMHO that is the only criteria for an appropriate punishment. A few years hard labor for the officers in charge and anyone who could possibly have prevented this. At the very least I consider it attempted murder, as if someone came through my door without warning the only question would be if I used my Colt 357, 12 gauge or 300 win magnum; Somebody would have died, maybe me, thus attempted murder (I don't believe in degrees of such a crime- you took actions that might, conceivably led to the death of an innocent party it's attempted murder in my book. But since I don't believe in reform or redemption the only purposes of the law are retribution and prevention.
There are some nuts who think that any effective blowback will paralyze all policing -- nonsense. This was as egregious an error as driving down the wrong side of the highway.