Thorgalaeg
Deity
I think the first suspect should be the pilot monitoring, since the pilot handling is too busy keeping the aircraft on the path. Usually it is the first officer who handles the aircraft during taking off and landings to add hours to his logbook while the captain is monitoring. So I would investigate the captain first.Yeah, the voice recording doesn't really prove whether it's the alleged culprit being asked, or if he asked his co-pilot the question to place blame away from himself.
I don't envy the investigators tasked with figuring it out. They'll have to investigate both pilots, their family situation, financials, medical history and so on with a microscope.