A gunman killed a Metro employee and injured three others during a random shooting spree in Washington, D.C., Wednesday morning. The shootings started when the gunman got into an altercation on a public bus, where he randomly shot one victim in the leg around 9 a.m., authorities believe. Another victim was reportedly shot as they were attempting to purchase a metro card at the nearby Potomac Metro Avenue Station. A metro worker was ultimately killed when he tried to help a woman the gunman had accosted—and was potentially trying to rob—at a station platform. “The fact that our citizens have to intervene with an armed gunman is disturbing to me,” said Ashan Benedict, the Metropolitan Police Department’s executive assistant chief of police. The gunman is in custody but police haven’t yet revealed a motive for the attacks. “We have a gun violence problem in America, and sometimes unfortunately that comes into Metro,” Randy Clarke, general manager and CEO for the Washington Metropolitan Area Transit Authority, said. “But this is not a Metro-specific safety issue. It's an American gun violence issue.”