He's a terrorist, he's helped plot multiple terrorist attacks that killed US citizens.
You can either send military forces to bring him in for trial. Which will take time and during that time more US citizens could be killed because he's on the loose.
Or, you can take him out with a drone strike, thus saving innocent lives.
You honestly think he's going to let the US take him in without a fight and want to go to court?
Fuck no, he's going to resist and fight for his life and end up killing more people. Take him out regardless of being a US citizen or not. Hell, he's not a US citizen in my eyes if he's killing fellow citizens in mass numbers.