We are speculating based on partial information from an unnamed source which I believe is a no-no in the forum. :-)

We still don't know the nature of the locking and the entry attempted except for one blabbermouth investigator who jumped the gun.

I assume the door is automatically locked when a pilot leaves. How do they normally get back in? I suppose they knock to have the other pilot let them in. If the pilot didn't respond, I assume they have some means to open the door from the outside unless it is overridden from the inside. We don't know for sure but can only speculate if the latter was the case as opposed to some kind of structural destruction inside the cockpit that knocked out the pilot inside and jammed the door.

Not saying it was definitely the latter either but I would think respect for the pilot and his family would discourage one to speculate prematurely in that direction with partial information until it is verified and officially determined, no?