I just saw a profile of the pilots on CNN. The co-pilot is a young-ish man and has been photographed smoking AND carousing with ladies in the cockpit.
The plane seems to have exhibited a pattern of flying that is intentional (sharp turns and a gain/loss/gain/loss in elevation) and under the control of SOMEONE.
In a 777 flight simulator, CNN reporter Martin Savidge sitting in the co-pilot chair, easily turned off the transponder beacon. Could do it with little notice from the pilot.
I think the co-pilot was under pressure (real or imagined) and in fear for his job/career as a result of "indiscretions". He cracked, folded, went crazy, choose your descriptor.
Well, that is what I think at 6:07pm Eastern on March 14.