Yeah, its war, but this was a US citizen. He was allowed to be assassinated without trial, against the constitution, against his natural rights, for goodness sake. That's just plain wrong. Especially if it would have been an easy conviction, as you imply. Convict him in a heartbeat, then execute him ASAP. Problem solved and you do things the lawful way without alienating voters who fear you're increasing wartime powers way more than necessary.