"There is no more "he said/she said" with a Tesla. That car will tell investigators everything."
The car won't lie, but its only as good as it's sensors and programming.
Scenario -- Car hits a concrete wall, catches fire, and partially burns out.
Driver -- car didn't stop when I hit the brakes.
Car logs - driver didn't press on the brakes.
Reality - the brakes WERE depressed; the brake pedal sensors failed and then burned in the fire); and as far as the car's logging system is concerned the brakes were not used prior to the crash.
This kind of failure happens all the time. The self-test reports its fine, but it still doesn't work. The self-test reports it's fine, but its still not sending events properly. The sensor itself is fine, but the events are getting swallowed somewhere else along the way. Or the self-test is fine at cold while idling, but get it scorching hot after a few laps and things start flaking out... add in 10 years wear and tear, humidity, rain, spray, and the ravages of time on rubber, seals, lubricants, sealants... and you really want to bet that the computer log of what happened is infallible?
Its just a new witness to the event, it's more credible than a human in many ways; some of the time; but it's not infallible.