The National Transportation Safety Board dispatched a go-team to investigate the collision of two Metro trains in Washington, DC., according to a press release issued by NTSB.

At approximately 5:00 p.m. ET Monday, two Washington Metropolitan Area Transit Authority trains collided on the Red Line. Nine people, including one of the train operators, were killed. The rush-hour crash injured more than 70. It was the worst crash in the Metro system’s 33-year history.

Railroad Investigator Ed Dobranetski is Investigator-in-Charge and is leading the team, which includes two specialists from the NTSB Office of Transportation Disaster Assistance.

After traveling about eight miles on the Red Line track, the moving train smashed into another train that was stopped. The trailing train, operating under automated control, barrelled into the stopped one and fell on top of it. Investigators are trying to determine why the train didn't stop. Evidence points to the emergency brake control being pushed down by the train operator before the crash.