The National Transportation Safety Board says a trainee was operating the train that struck and killed two BART workers.
BART officials initially said an experienced operator was at the controls of the train at the time.
Laurence Daniels from Fair Oaks and Christopher Shepherd were struck and killed while they were inspecting the tracks between Walnut Creek and Pleasant Hill.
The NTSB will conduct a re-enactment of the accident to learn more about what happened, but they haven't said when it will take place.
Meanwhile, BART and its striking unions are hoping to reach an agreement before the Tuesday morning commute.