Assistant Chief Constable Anthony Bangham says witnesses had reported dense smoke that made driving almost impossible at the scene of Friday’s collision on the highway in southwestern England.

He said Sunday police are now investigating a fireworks show that took place around the time of the fatal crash. The fireworks display was one of many organized over the weekend to mark Guy Fawkes Day, an annual commemoration of the English revolutionary who tried to blow up Parliament in the 17th century.

Police say they have finished removing all vehicles from the highway in Somerset, but roads have not yet reopened.