Dried ears
This has been addressed numerous times
If locked and timing out the 30 sec buzzer does not sound
He probably locked it as soon as the cpt left the cabin
And a few times while he was trying to get in
The buzzer would never sound
It only sounds if in 'auto' mode to give the crew to verify ID
The door was locked
The plane was piloted into the ground
The ap alt was reset to 100'
The fo was alivecand breathing
Never requested help
All this in a few minute period
It took 8 minutes
The time out was 5
So if he was incapcitated and accidently locked the door the cpt could have gotten in after the 5 minutes expired
Since he could not it means the fo hit lock again
It's clear what happened