They had been coworkers. They had been friends. Mark Barton seemed personable, friendly and trustworthy when he began working at Brent Doonan's day trading company, All-Tech. When he began to lose money he vanished. When Barton reappeared it was to repay his debt in a way that no one could have expected. In a blaze of bullets and blood, Baron killed four Momentum employees and wounded seven others. He then calmly crossed the street to All-Tech, paid his old friend Brent a visit and shot him five times. He went on to kill five more people and wound an additional six in the worst incident of workplace violence in history.