Here's a video of a Tesla owner Sergio Rodriguez activating AP on a nothing street with no lines. AP sets itself to 45mph which he says is too high. AP proceeds to accelerate and fails to react to the curve except he stops it. Whether this video has any bearing on the crash in Texas it is interesting allowable behavior in the car. It seems to do what we are told Tesla's on AP cannot do.
Let's say the car "backed from the driveway" and started driving as we were told in witness statements. One guy in the back, one guy in the front. Some form of disable devices in the seatbelt and/or seat weight. Whatever was required. Let's suppose that starting position is halfway up the driveway at #2 Hammock Dunes Pl for the sake of argument, where there is a reddish car on Google Maps. Not sure if that is the correct house, but let's start there.
They back from the parking spot and drive down the driveway, through the cul de sac and down the street. Total distance is 450-550 ft. Somehow they have enabled Autopilot - as Sergio Rodriguez was able to do in his video. The Tesla "should" not allow this, but does anyway - as Sergio's car did. Let's say it accelerates to 45mph either given a nudge from the passenger's foot or by itself. Perhaps they entered a higher speed or resumed a previous set speed. Again, the Tesla "should" not do that, but perhaps they discovered that it actually does - as Sergio Rodriquez did. Perhaps they get it up much higher than 45mph.
Next, either AP fails to make the turn - like Sergio's car, or they nudged the wheel by mistake, disabling AP and it doesn't even try to turn. If they "nudged it off" then AP would show as not engaged, as Elon said.
45mph is not very fast, but perhaps fast enough to crash into the tree injuring the occupants. Perhaps they were not belted. Perhaps running over the curb/drain and hitting the tree was enough to cause an instant fire. Perhaps the fire was so sudden that though just injured they were incapable of escaping. Perhaps the passenger's seat was wedged against a tree, the battery had failed and the rear passenger didn't know the escape procedure. Perhaps 45mph was fast enough. Lots of "perhaps" I know, but it fits the scenario.
Just reconciling the witness statements with the list of possible reasons they might have tested the car in this manner. They wanted to see the car navigate on AP on their little street (maybe the owner had previously found that it would do it, even though it's not supposed to be able to do it). It seems AP
can activate on streets with no lines. It seems the car
can accelerate to an unsuitable 45mph on a small street. It seems the car on
AP can fail to turn whatsoever on those streets (thanks to Sergio Rodriguez's video).
Would not be good for Tesla if AP could/did actually do all these dangerous things that Tesla claims it would never do.