How common is it for captains to leave their seats and flight decks on such a short sector? If it is relatively uncommon, then the FO (if it is proven to be by his hand) must have either been considering this action for a number of flights, or just took his opportunity on the spur of the moment.
Is it too simplistic to say there would/might have been signs that all was not well with this young pilot?
DUD-BCN-DUS I would say, at some point, very likely.
On the turnround there is much to do, the cleaners are in the toilets, the water doesn't work to wash hands, no air conditioning.
I am not a psychologist, I'll fly with a different colleague most days, and we have grown up in different eras, possibly cultures etc. The slightest query to or about someone will result in a bullying and harassment accusation re racism / sexism. We are actively taught in our airline to be "tolerant" of everybody, which equates to me the opposite of seeking out potential issues.