A white gunman livestreamed a racially motivated mass shooting online, showing himself killing 10 people and wounding three others Saturday at a Buffalo, N.Y., supermarket in a historically Black neighborhood.The suspect has been identified as Payton Gendron, 18, of Conklin, N.Y.According to witnesses and law enforcement, the gunman was dressed in body armor and armed with a high-powered rifle as he livestreamed the massacre. Investigators were reviewing a hate-filled manifesto the suspect apparently posted online.U.S. Rep. Brian Higgins, whose district includes parts of Buffalo, said the gunman had a racial epithet on his rifle. “It was straight up, a racially...