Swiss prosecutors have begun looking into the circumstances of a fatal crash of a Tesla electric car last week that firefighters think may have set off a fire in the vehicle’s battery.

A spokesman for prosecutors in the southern canton of Ticino said authorities were examining what led to the accident. It was too early to discuss the cause at this stage, he added.

“So far the only thing for sure is that there was an accident with a Tesla,” he said, declining to say when results of the investigation are expected.

Swiss firefighters said on Monday that the impact in a fatal accident involving a Tesla electric car may have set off a fire in the vehicle’s battery.

A 48-year-German driver died when his car hit the barrier on the central reservation of a motorway in Ticino, rolled over and burst into flames.

The crash on Thursday is one of several accidents to affect Tesla vehicles in recent days.

“The violent impact of lithium-ion batteries could probably have caused a phenomenon called ‘thermal runaway’, ie. a rapid and unstoppable increase in temperature,” the Ticino fire brigade had said on its Facebook page.

A Tesla spokesman had said: “We are deeply saddened by this accident and we are working to establish the facts of the incident and offer our full cooperation to local authorities.”

On Friday a Tesla Model S crashed at speed into a truck in South Jordan, Utah.

The U.S. National Highway Traffic Safety Administration (NHTSA) is also reviewing a Florida crash of a Tesla vehicle last week, resulting in the death of two teenagers.