Mark Orrin Barton (April 2, 1955 – July 29, 1999) was an American spree killer from Stockbridge, Georgia, who killed twelve people and injured many more on July 29, 1999. The murders occurred at Barton's home as well as at two Atlanta-area day trading firms, Momentum Securities and the All-Tech Investment Group, where he had previously been employed as a day trader. It is believed that Barton was motivated by large financial losses incurred during the previous two months. Barton killed himself before he could be apprehended by police.