http://www.history-sites.com/cgi-bin/bbs62x/mocwmb/arch_config.pl?md=read;id=3609

This original post is a decade old. I happened to come across it while researching something entirely different. There is another source that seems to corroborate the newspaper's report of the death of General Lyon. Years after the war, Brevet Brigadier-General, William M. Wherry, Sixth U.S. Volunteer Infantry, wrote about the battle for “Battles And Leaders Of The Civil War:”

"Lyon repeated his order for the regiment to come forward. The regiment moved promptly by the flank, and as it approached Lyon he directed the two companies of Iowa troops to go forward with it, himself leading the column, swinging his hat. A murderous fire was opened from the thick brush, the 2d Kansas deployed rapidly to the front and with the two companies of the 1st Iowa swept over the hill, dislodging the enemy and driving them back into the next ravine; but while he was at the head of the column, and pretty nearly in the first fire, a ball penetrated Lyon’s left breast, inflicting a mortal wound. He slowly dismounted, and as he fell into the arms of his faithful orderly, Lehmann, he exclaimed, “Lehmann, I am killed,” and almost immediately expired. Colonel Mitchell was also severely wounded about the same time and removed to the rear."

Here and in the newspaper's report, The Union Officer killed was "mounted" and "waving" or "swinging" his hat."