BOSTON (AP) — One of four operators on board two Green Line trains that collided on Friday and injured more than 20 people has been place on paid administrative leave.

A spokesperson for the Massachusetts Bay Transportation Authority, Joe Pesaturo, declined to identify the operator, but said the decision was made Saturday based on developments in the ongoing investigation, according to the Boston Globe.

The operator was piloting the first car of the two-car trolley that struck another Green Line train from behind. The operator has worked for the transit agency for seven years.

The four MBTA operators were among the injured.

Train service along the Green Line resumed Saturday.