Crash investigators do this for a living?

Great to hear that she is doing well. It must have been very difficult to arrive on such a scene.

No one rolls a window up at the scene of an accident, it's not logical in the moment, and any officer that would do that is tampering with evidence I would imagine.

My sister was in a horrible crash once, seat belt left marks/bruses, even with air bags going off.

Thanksgiving eve I went to bed at 2 am, working on house all night. 3 am wife wakes me, 2 guys are trying to break in, enraged and going from door to door, long story short, one drives away, other stays, cops show up and want to immediately take him and go. Not concerned about potential damage, won't tell me his name, not interested in locating the car that just left, etc.
Filed a foil request, got the run-a-round, report never filed, no arrest, finally got a copy. Two military guys had the wrong house, drunk, mad, cold, report states they took him home and helped him into his house. Didn't mention if they tucked him in.
If a friend and I did that at his house we would at a minimum be in the clink over night, and probably multiple charges.

Point being, sometimes conclusions are made and actions are taken based on who you are and who you know.