SEATTLE (AP) — A rail union official reportedly told investigators that a fiery oil car train derailment in western Washington late last year was caused by sabotage.

Seven train cars carrying crude oil derailed and five caught fire in the town of Custer on Dec. 22, sending a large plume of black smoke into the sky close to the Canadian border.

There were no injuries in the derailment, but KUOW reports that an official with the union representing the driver has told authorities the derailment was not an accident.

The incident happened near where two people had been arrested a month before and accused of attempting a terrorist attack on train tracks to disrupt plans for a natural gas pipeline.