A simple revision is to reserve the death penalty to those who are convicted of murders that took place on two separate days. The Boston bomber falls into this category as do serial killers. It also resolves the question of what to do with a prisoner serving a life sentence who kills a prison guard.
How does the Boston Bomber fit this category? Regardless, it creates a glaring and unfair contradiction. A bomber who kills 20 people instantaneously isn't subject to capital punishment, but a shooter who hits two people, one of whom dies directly while the other one hangs on until 12:01 am the next morning, is subject to potential execution.
