A gunman in a gas mask and construction vest set off a smoke grenade and fired a barrage of bullets in a rush-hour subway train, shooting at least 10 people Tuesday, authorities said. Police were trying to track down the renter of a van possibly connected to the violence.

Police Chief of Detectives James Essig said investigators weren’t sure whether the man, identified as Frank R. James, 62, had any link to the subway attack.

Authorities also were looking into social media posts by someone with the same name that mentioned homelessness, New York and Mayor Eric Adams, leading officials to tighten the mayor’s security detail, Essig and Police Commissioner Keechant Sewell said. She said the posts were “concerning.”

The attack made the subway a scene of horror: a smoke-filled car with at least 33 rounds of gunfire going off, police said. Frightened commuters ran from the train and others limped out of it. At least one rider collapsed on the platform.