MBTA officials say they've found no mechanical problems with the Green Line train that derailed Monday, leaving seven passengers with minor injuries.
The track and signal systems were also inspected and no defects were found.
MBTA spokesperson Joe Pesaturo says the focus is now on the train operator.
"Investigators continue to take a close look at the performance of the motorperson who was operating the train at the time." Pesaturo said in a statement.
The Boston Globe reports that the train operator, who has worked at the MBTA for four years, has been "removed from service" during the investigation.
Around 12:20 p.m. Monday, a Green Line train bound for Riverside crashed into a tunnel wall after derailing between Kenmore and Fenway stations.