We knew it: the Boston commuter train that left the station with a driver yesterday didn’t suddenly become self-aware and decide to drive off all on its own. Instead, investigators reportedly found a cord wrapped around the train’s accelerator.

On Thursday morning, a Red Line train rolled away from the station with 50 passengers aboard and made it through four stations before humans were able to stop it.

After the incident, the Massachusetts Bay Transportation Authority said it seemed likely that someone had deliberately messed with the train, and a new report indicates that’s the case: WBZ-TV cites sources familiar with the investigation that a rubber telephone cord was used to inhibit the normal movement of the train.

It was reportedly wrapped around a control called the Cineston valve, which acts as either an accelerator or a brake control. It requires constant pressure to set the train in forward motion.

The train’s operator stepped outside to set a bypass switch because of a signal problem, but the cord hadn’t been removed, which made it keep going without him, the sources say.

Transportation Secretary Stephanie Pollack would not confirm the cause Friday to WBZ-TV, citing the ongoing investigation.

The conductor involved was brushed by the train and suffered a minor leg injury. He’s now been placed on administrative leave pending the outcome of the investigation.

The MBTA says going forward, it will require the presence of a second technician during a bypass procedure, instead of relying on a single operator to man the train.

Cord Reportedly Found Wrapped Around Accelerator Of Runaway Red Line Train [CBS Boston/WBZ-TV]

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