In the course of my youtube surfing the other day, I came across a (very cheaply done) CGI video relating how a British Special Forces sniper team did something like that (in 2009 IIRC).

The team crept quietly into an area where the Taliban had started a training camp, setting up on a rooftop some 500 meters outside the camp. Over the course of several days of observation, the team noted an apparent VIP - dressed in flowing robes of pristine white - regularly visiting the camp to harangue the recruits. On one particular day, the sniper on duty saw this VIP begin to demonstrate how to chop off heads, using a variety of implements.

The sniper carefully put a single bullet through the VIP's head, exploding it's contents all over the lined-up recruits, causing them all to run screaming.

Attendance at that camp dropped to almost nothing immediately thereafter.