If he’s locked up in prison with fellow Muslims, then it will merely encourage others who seek righteousness by their own hand in their own eyes, to commit similar heinous criminal acts.
IMHO, the death penalty is warranted to preserve freedom for the public from similar criminally minded Islamic extremists, regardless their country of origin.
Teller could have really helped him "out"!
That white guy needs to spend a LOT more time in the weight room...