Tesla Motors Inc told U.S. Senate Commerce Committee staff it is considering two theories that may help explain what led to the May 7 fatal crash that killed a Florida man who was using the car’s “Autopilot” system, a person familiar with the meeting told Reuters on Friday.

Tesla staff members told congressional aides at an hour-long briefing on Thursday that they were still trying to understand the “system failure” that led to the crash, the source said.

Tesla is considering whether the radar and camera input for the vehicle’s automatic emergency braking system failed to detect the truck trailer or the automatic braking system’s radar may have detected the trailer but discounted this input as part of a design to “tune out” structures such as bridges to avoid triggering false braking, the source said.

Tesla declined to discuss the meeting except to say it did not suggest that the vehicle’s cameras nor radar “caused” the accident. It was not clear if other factors were under investigation.

Joshua Brown was killed when his vehicle drove under the tractor-trailer. It was the first known fatality involving a Model S operating on the Autopilot system that takes control of steering and braking in certain conditions.

Tesla Chief Executive Officer Elon Musk was asked on Twitter why the radar did not detect the truck. Musk wrote in a June 30 tweet that “radar tunes out what looks like an overhead road sign to avoid false braking events.”

Tesla said in a June blog post that “neither Autopilot nor the driver noticed the white side of the tractor-trailer against a brightly lit sky.”

Tesla confirmed that the briefing occurred, but a spokeswoman declined to comment on what transpired.

The source said Tesla also told committee staffers it views braking failure as separate and distinct from its “Autopilot” function, which manages steering, changing lanes, and adjusting travel speed.

On Tuesday, the U.S. National Transportation Safety Board (NTSB) said its preliminary findings showed the Model S was traveling at 74 miles per hour (119 km per hour) in a 65-mph (104 km per hour) zone at the time it struck the semi-truck near Williston, Florida.

The report said the NTSB confirmed the Model S driver was using the advanced driver assistance features Traffic-Aware Cruise Control and Autosteer lane-keeping assistance at the time. The NTSB has not yet determined the probable cause of the crash.

Tesla faces a separate investigation by the U.S. National Highway Traffic Safety Administration (NHTSA) into whether the system poses an unreasonable risk to driver safety. It faces a Friday deadline to answer the safety agency’s initial questions about the crash.