A digital video disc player was found in the Tesla car that was on autopilot when its driver was killed in a collision with a truck in May, Florida Highway Patrol officials said on Friday.

"There was a portable DVD player in the vehicle," said Sergeant Kim Montes of the FHP in a telephone interview. She said there was no camera found, mounted on the dash or of any kind, in the wreckage.

A lawyer for a truck driver involved in the accident with the Tesla told Reuters his investigators had spoken to a witness who said the DVD player was playing a "Harry Potter" video after the accident, but the lawyer was unable to verify that beyond the witness account.

"As to the video, there was a witness who came to the scene immediately after the accident occurred, and we can't verify it at this point," said Paul Weekley of Tampa, the lawyer for the truck driver. "But what we have been told is that he saw a Harry Potter video still playing when he got to the scene.

Lawyers for the family of the victim, 40-year-old Joshua Brown, released a statement Friday saying the family is cooperating with the investigations "and hopes that information learned from this tragedy will trigger further innovation which enhances the safety of everyone on the roadways."

The statement describes the accident as having been "caused by a semi tractor-trailer which crossed a divided highway and caused the fatal collision with Josh's Tesla."

The questions surrounding why the 2015 Model S Brown was driving did not stop for the truck, and whether Brown was watching the road at the time are critical for Tesla Motors Inc. The electric car maker is facing a preliminary inquiry by federal regulators over the safety of the Model S Autopilot system that was engaged at the time of the crash.

Tesla shares fell in after hours trading Thursday after the fatality was disclosed, but rebounded to close up nearly 2 per cent in trading Friday.

The Autopilot system allows the car to keep itself in a lane, maintain speed and operate for a limited time without a driver doing the steering.

Tesla said in a statement Friday, "Autopilot is by far the most advanced driver assistance system on the road, but it does not turn a Tesla into an autonomous vehicle and does not allow the driver to abdicate responsibility."

It could be weeks before officials make a final determination of the cause of the crash, the first known fatality of a Model S driver while using Autopilot.