Nick Vaccarezza remembers the moment he knew it was not a drill. The pop-pop-pops coming from the freshman building at Marjory Stoneman Douglas High School in Parkland, Fla., were the real thing – gunfire – because Nick had fired a gun before. With his younger brother Mike safely under his wing, Nick and a friend turned to each other and said, “Let’s go.” They bolted away from the ballfield dugout that was their shooter drill evacuation zone and hit the eight-foot fence at the school’s perimeter on the fly, then made a beeline to the Wal-Mart Supercenter a long block to the west.