An article on the death penalty in Texas, "Religion and Culture Behind Texas Executions", we find his passage.
[T]hey also find justification in scripture. "A lot of evangelical Protestants not only believe that capital punishment is permissible but that it is demanded by God. And they see sanction for that in the Old Testament especially," said Matthew Wilson, a political scientist at Southern Methodist University in Dallas.
So, somebody reads in their holy book that others shall die and, on that basis, takes it to heart to do the killing.
I would like an explanation as to how this is different than using scripture to justify flying airplanes into sky scrapers, or setting off bombs in Madrid trains, London busses, Baghdad shopping centers, Israeli malls.
Fundamentally, these people are all alike in their lust to kill in God's name.
And if the answer is, "Oh, but the people that I kill when I appeal to scripture are only those who deserve death," my response will still be, "Don't you think that those others say the same thing?"