Simple. The death penalty was eliminated in civilised countries many years ago. Somehow the American love of revenge and slaughter has kept it in the US. As to sending the guy to Guantanamo Bay or declaring him an "enemy combatant", that's just silly. I'm not sure that the term "enemy combatant" has any validity in American civil law or even military courts in the US and I'm even more doubtful that Trump could legally send anybody to Gitmo bypassing the American legal system. The only way prisoners got to Guantanamo Bay was being spirited away from battlefields in controvention of international and US law. Apart from that you're quite right :-)