Yesterday, Michael Brandon Hill, a 20-year-old with a history of mental illness, allegedly entered Ronald E. McNair Discovery Learning Academy, an elementary school in Decatur, Georgia, with an AK-47 and nearly 500 rounds of ammunition. Dressed in black, he'd slipped in behind someone authorized to be there and confronted Antoinette Tuff, a bookkeeper who'd just sat down temporarily to relieve the school secretary of her duty. This was serendipitous timing: Tuff is the one who ultimately convinced Hill to surrender before anyone was hurt.