General Stonewall Jackson, leading a large part of General Lee's army, delivered a devastating blow on General Hooker's right flank. Reconnoitering with his staff at day's end, Jackson and his group were mistaken for Union soldiers and fired on by their own forces. Jackson's shattered left arm had to be amputated. While he was hospitalized pneumonia set in; his death came on May 10.
Carruth, Gorton. "The Encyclopedia of American Facts and Dates". 10th Ed. New York: Harper Collins Publishers. ©1997.