Nine people died and 76 were injured—six critically—on Monday when a commuter train on D.C.'s red line, the Metro's busiest line, rammed into the back of a stopped train during rush hour. The dead include the operator of the trailing train, Jeanice McMillian, the Los Angeles Times reports. The front end of the rear train jack-knifed into the air and landed atop the stationary one, ripping open cars from both trains. According to The Washington Post, experts have several theories around the crash: the electronic failsafe system, which detects distances between trains may have failed in an episode similar to a near-miss crash on the Metro system four years ago. There is some evidence that a small portion of failsafe devices used by the Metro have manufacturing defects causing them to fail after 25 years instead of their projected 70-year lifetime. Operator error could also be responsible for the crash.