Rehabilitation in this case is all but a fruitless endeavor: Tsarnaev is unrepentant now and will almost certainly remain unrepentant in the years to come. Killing him while he is “unrehabilitated” would thus invalidate the very premise of the execution. (If it’s the threat of capital punishment that should cause Tsarnaev to “rehabilitate” sometime between now and the date of his execution, then the death penalty would be similarly meaningless: why execute someone for purposes of “rehabilitation” when it has already been achieved?)

Retribution is an equally nonsensical concept in this regard. Retribution comes from the Latin retribuere, “to pay back,” and it is just nonsensical to suggest that Tsarnaev can “pay back” anyone with his death. Who, precisely, holds the invoice for the murders he committed? To whom is his payment being conveyed?

Using the death penalty in self-defense in this case seems equally bizarre: Tsarnaev is a lot of things, but it is ridiculous to suggest he is a threat to anyone or anything other than his bedbugs at this point. Using lethal force against him while he was at large could have been justified; in prison, bound by the chains and the cells that will mark the rest of his life, claiming self-defense against this man is a non sequitur.

That leaves deterrence, and while there are some studies that purport to show that the death penalty does indeed deter future criminals, I find this to be a rather grisly recourse to take.