in edmond, oklahoma. >> many of patrick sherrill's co-workers called him "crazy pat." ly did not see him as a ticking time bomb. >> just after dawn on august 20th, 1986, sherrill reported as usual to the post office in uniform and carrying a mail bag filled with guns. >> two days earlier, his supervisor at the post office had threatened to fire him, and he decided he was going to get even. >> in the end, patrick sherrill killed 14 co-workers before killing himself. like patrick sherrill, mark barton was never formally diagnosed with a mental disorder. in hindsight, barton's personality fit clinical patterns of a man on the edge. >> the person that i started to work with and the person that he ended up were two different people. he was not the same person at all. >> secretary leigh ann burke saw mark barton's behavior change over time. she started working with him in 1984 in texarkana, texas, where he was employed as a chemist for tlc manufacturing, a company that made cleaners and solvents. >> he was always kidding around and laughing and making jokes in the beginning.