PALO ALTO (CBS / AP) -- A person familiar with the discussions says Tesla has told Senate committee staffers that its engineers have two main theories about what caused a fatal crash in Florida involving one of its electric cars in self-driving mode.

Either the car's cameras and radar failed to spot a crossing tractor-trailer. Or the cameras didn't see the rig and the car's computer thought the radar signal was false, possibly from an overpass or sign.

Tesla officials disclosed the theories a briefing with U.S. Senate Commerce Committee staff members Thursday, said the person, who didn't want to be identified because the meeting was private.

Government regulators are investigating the May 7 crash to see if Tesla's Autopilot system may have a defect. Neither the Autopilot nor the driver braked before hitting the rig.

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