In large part, the future of the transportation industry hinges on the efforts of companies like Tesla that are working to create autonomous vehicles. But that movement suffered a fairly major setback on March 23 when a Tesla Model X car slammed into a highway barrier on U.S. 101 and killed a driver in California. Now, in the wake of that crash, there is disagreement on what exactly caused the accident and who’s to blame.

Tesla has expressed condolences to the driver’s family, but has made little effort to take responsibility for the incident. Rather than criticize the design or engineering of its product, the company questioned whether the driver of the “semi-autonomous” car was paying attention. The company also pointed out faults in the “crash attenuator”—a highway barrier that is designed to reduce damage to vehicles or motorists in the event of a collision.

“We have never seen this level of damage to a Model X in any other crash,” Tesla said in a statement.

Meanwhile, federal investigators have said they’re “unhappy” with Tesla’s statements in the wake of the accident. The National Transportation Safety Board is looking into the accident and appreciates Tesla’s assistance, but isn’t fully satisfied with the explanations they’ve heard so far.

“Tesla has been extremely cooperative on assisting with the vehicle data,” NTSB spokesman Chris O’Neil said. “However, the NTSB is unhappy with the release of investigative information by Tesla.”

The NTSB investigation is a slow and methodical one, and so far the government agency is not ruling out Tesla’s explanations or design flaws in the Model X as possible causes of the crash. O’Neil emphasized that the board would investigate all aspects of the crash before reaching any conclusions.

This episode is part of an ongoing saga as America continues to debate whether autonomous cars will be a safe and viable option in the future. This is not the first time that a semiautonomous Tesla vehicle was involved in a fatal crash; another one was involved in a collision with a tractor-trailer in 2016.