Suicidal Terrorists
If these lower life forms are determined to commit multiple murder as they suicide for some belief or other, I don't think the death penalty is inappropriate if they are prevented from completing their actions. At the very least, they won't be around to try it again or train some other misguided wally from attempting the same insane outrage.
I agree the death penalty is the ultimate form of punishment but it should still be available in cases of "no doubt what-so-ever guilt" of outrageous, horrendous crimes.