Federal safety regulators have sent a team to investigate the fatal crash of a Tesla electric car in a Houston suburb in which no one was behind the wheel.

The National Highway Traffic Safety Administration (NHTSA) said on Monday it had sent a special crash investigation team to Spring, Texas.

Investigators are “100% sure” no one was driving the 2019 Tesla Model S on Saturday night when it ran off a road, hit a tree and burst into flames, killing two men inside, Constable Mark Herman of Harris county precinct four said.

One man was found in the front passenger seat and the other was in the back seat.

KHOU-TV reported that the car was a 2019 Tesla Model S, and the men were aged 59 and 69.

The NHTSA has sent investigators to 27 Tesla crashes in the past few years.

In Texas on Monday, investigators were still trying to determine whether the electric car was operating on the Autopilot driver-assist system or if the Full Self-Driving Capability system was in use.

In a statement, the NHTSA said: “We are actively engaged with local law enforcement and Tesla to learn more about the details of the crash and will take appropriate steps when we have more information.”

Investigators were also working with the National Transportation Safety Board (NTSB) and getting search warrants seeking evidence in the crash. Herman would not say if those were directed at Tesla. He said he did not know if investigators had spoken to the Palo Alto, California, electric vehicle maker.

Tesla’s Autopilot partially automated driving system has been involved in several fatal crashes, for instance failing to spot tractor trailers crossing, stopped emergency vehicles or a highway barrier.

The company has said drivers using Autopilot must be ready to intervene at any time. It says the Full Self-Driving Capability system cannot drive itself and must be continually monitored.

The NTSB has recommended that NHTSA and Tesla limit the roads on which the systems can safely operate, and that it install a more robust system to monitor drivers. Neither Tesla nor the agency took action.

In the latest crash, investigators had not determined how fast the Tesla was driving. Herman said it was a high speed.

He would not say if there was evidence anyone tampered with Tesla’s system to monitor the driver, which detects force from hands on the wheel. The system will issue warnings and shut the car down if it does not detect hands. But critics say it is easy to fool.

A message was left on Monday seeking comment from Tesla, which has no media relations department.