IFF ...

If the perp is truly tribal and he has actually sworn fealty to the Yemeni leader as reported, then he is no longer a threat. Within that cultural context, he has behaved properly against his enemies. By publicly renouncing his fealty to Bin Laden and the goals of Al Qaeda, he has switched sides from active enemy to a more or less neutral party.

Also within his tribal view is the fact that he has not satisfied his enemy's desire for justice (that would be us). Now if we were to play by their tribal rules we would demand that he also swear peace with us (he can only have fealty to one leader at a time so we would get nowhere requesting that). If he received our demand he would then open negotiations for terms of peace. If both parties agreed to some final terms then he would no longer be a threat, so long as we upheld our side of the bargain.

That's how a feudal culture works.

B