Reading his Wikipedia, it seems he was guilty of hate speech against the country, and his connection with committers of violence was through writing and "inspiring".

If that's treason, then I suppose a future leftist Castro-esque president should be free to drone-murder hate speech mongers like Rush Limbaugh and many in the Fox News commentary department.

America likes to talk about respecting democracy and the rule of law, but the way it acts is nowhere near that.