hi clo,
with one pilot locked out of the cockpit, all sorts of new scenarios are in play.
i thought you always had two people in the cockpit at one time. but i am no airline pilot. if it isn't two people being incapacitated at the same time, then you are looking at the actions of a single person.
so any kind of personal issue is in play. resentment can make folks do strange things. heck, even malicious hypnosis could be responsible.
that door needs a further emergency override. maybe from ground control.