The only way Cabin crew should be allowed access to the flight deck is by training them for that role. Designating certain Senior Cabin crew with a track record of at Least 3 to 5 years with the Airline.
Agreed on that one, they also need a good understanding of what goes on if they are expected to detect the unusual. Would a cabin crew member have intervened in this case when the FO dialed an altitude and pulled the knob to descend? I suggest not until too late.
A shrink may be able to expand but I guess suicide is a lonely thing and maybe someone else on the flight deck would break that mind set, whereas alone on a locked flight deck he is on his own to do as he pleases. Any shrinks on?
Also, you always hear breathing on CVRs because the mikes are 'hot' to the CVR.