The fatal crash of a Tesla with no one apparently behind the wheel has cast a new light on the safety of semiautonomous vehicles and the nebulous U.S. regulatory terrain they navigate.

Police in Harris County, Texas, said a Tesla Model S smashed into a tree on Saturday at high speed after failing to negotiate a bend and burst into flames, killing one occupant found in the front passenger seat and the owner in the back seat.

Tesla Chief Executive Elon Musk tweeted on Monday that preliminary data downloaded by Tesla indicate the vehicle was not operating on Autopilot, and was not part of the automaker's "Full Self-Driving" (FSD) system.