The driver had his hands off the wheel for all but 51 seconds of the last 14 minutes A/P was engaged, and either had a bagel or a cup of coffee in one hand, plus was distracted by the radio. The report goes into detail about how the A/P warning system works, including the fact that on a divided highway you can go 3 minutes hands-off before a warning is issued, if there is a lead car, and 2 minutes otherwise. The first audible warning is issued 15 seconds after the visual warning, the second 10 seconds after that, and the third 5 seconds later, at which point the car begins to decelerate. In other words, you can go at least (see below) 3 min. 30 seconds with your hands off the wheel before the car will assume no one's paying attention.
The car had hardware v1.0 and firmware 17.50.97-3bd9f6d082U, installed on 12/28/2017. Some of the warning times have apparently changed in later versions of hardware and firmware. The total trip was 66 minutes, and A/P was engaged for a total of 29 min. 4 sec., with hands detected on the wheel for only 78 sec. total. During the last A/P segment, visual hands-off alerts were issued four times,, and no hands were detected for the last 3'41" before impact. This was possible because the car's speed dropped below 25 mph at some point, which allows up to 10 minutes before a warning is issued. The Tesla slowed to 21 mph behind the lead vehicle.
When the lead vehicle changed lanes to avoid the fire truck 3-4 seconds before impact, the Tesla began to accelerate to the TACC set speed of 80 mph (speed limit is 65). At 0.49 sec. before impact the FCW detected a stationary object (the fire engine) and issued audible and visual warnings to the driver. The Tesla was doing 30.9 mph at impact. AEB didn't activate nor would it as it's known that it can't deal with this situation.
To what should be no one's surprise, this is another confirmation that A/P as implemented not only allows but even encourages driver disengagement, just as all the research indicated would be the effect of such an implementation.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].
The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.