What about the Due Process demands of the Fifth Amendment?
When you get past that.....and a Court agrees with you....Doom on them!
Until you do....like it or not...he is fully entitled to that protection under the law.
If he is in a combat zone...say Afghanistan or Pakistan, is caught carrying a weapon, planting an IED, or conducting an armed attack...do him in anyway you can. If you catch in the act inside the USA...again pop him. If not in the act....arrest and prosecution in court is the right way...if he resists with a weapon....pop him. I am old time law enforcement....I have no hang up over dusting a bad guy but you have to do it legally.
As cold as it sounds, a Non-US citizen in exactly the same situation....riding in a car in the desert does not enjoy that same protection as they are not US Citizens....granting them that might be a consideration.
Riding in a car, in the middle of the Yemeni desert lands, I feel you have not reached a threshold that allows you to pop him.