You want time to recover data, investigate the physical condition of the aircraft/vehicle, etc.
How thorough of the job can the police do in the dark from 9:30pm-1:30am?
This completely looks like a special snowflake exception that Cruise, given its behavior afterwards, should not have had... and at this point, should not be trusted to have again.
It is important to remember I think that to the police officers this is just a day in their job they are clocking in and out. They are just following their instructions. It might be life changing for someone who got hit but the world just keeps spinning.
What's to stop Cruise or other bad actors to take possession of the car and then clip the brake lines to claim it was actually an OEM vanilla car mechanical fault and not their AV hardware/software?
It's not that outlandish. You already have them doing a whole bunch of lies of omission and smoke screening their video evidence, enough so to trigger a wave of resignation/firings.
And just like that they lost all interest in the situation.
Unrealistic take: The police should have kept the vehicle and demanded the source code be released so that it may be investigated if proper safety mechanisms have been implemented and if any errors in the systems may have caused it to hit the pedestrian. In the meantime the vehicles running on the same hardware and software should be put on probation.
Realistically: Police cannot investigate this and as long as these vehicles are classified more like computers and less as an aircraft these incidents are "glitches".
Presumably that happens because the NTSB want to examine the airplane. In this case there was no equivalent organization to the NTSB run by the Police and nothing about the car that needed to be examined by the Police to establish what had happened.