How did the Headless Horseman lose his head?

The legend of the Headless Horseman begins in Sleepy Hollow, New York, during the American Revolutionary War. Traditional folklore holds that the Horseman was a Hessian trooper who was killed during the Battle of White Plains on 28th October 1776. He was decapitated by a cannonball, and the shattered remains of his head were left on the battlefield while his comrades hastily carried his body away.

Source: Wikipedia