If he wasn't, too bad for the values of our enemy...that doesn't mean WE have to stoop to their level.
Procedures to follow, in a nutshell.
If Al-Qaeda, try, prove, find guilty or innocent, and either IMPRISON (if guilty) or release (if innocent).
If legitimate POW, hold in appropriate facility humanely with oversight from Congress and SCOTUS, and release after end of our wars.
Simple LEGAL procedures we can follow that maintain our national security AND maintain our rule of law/values.
IF... for God's sake he was beheaded, had his internal organs ripped out his body, had his eyes gouged out, and his private parts cut off.