Metro’s general manager said the transit system was manually checking all of the some 3,000 circuits in the rail system after a National Transportation Safety Board investigation pinpointed one as having “anomalies” along the tracks near where a train slammed into another Monday, killing nine and injuring more than 70.

The NTSB said Thursday that the sensor system, which helps control the speed and placement of trains, did not detect a test train standing in the same spot as the train that was hit. That indicates it may not have been able to sense that a train was stopped on the tracks ahead.