The amount of 'security' that pax should be subjected to will plainly fluctuate as does the 'threat level.
For aircrew, however, the sole purpose of contact with 'security' is to give the crew member whose family are being held hostage, a chance to express their concerns unobtrusively to someone who is in a position to help.
I can see no other reason to detain aircrew, who will soon have total control of the aircraft and all the pax anyway.