Sky marshalls or Air Guards as they used to be known as used to fly as plain clothes pax on the airline that I work for.They could be spotted from a mile away sitting in First Class ordering the Cabin Crew around and asking for refills periodically.The appearance of a military man even without uniform is pretty easily distinguishable with a Crew cut hairstyle and some having curled up moustaches.One of my friend happened to be occupying the seat adjacent to the Air Guard once and narrated a horrifying incident.The Air Guard apparently after completing his 10 COURSE MEAL dozed off and his loaded gun slid out of his pocket onto the floor without him realizing it.My friend picked up the gun and put it behind the magazines in the rack upfront.When the Air Guard got up,he instantly felt for his gun which was not there and freaked out.While conducting a frantic search for it he questioningly looked at my friend and my friend asked him what seemed to me wrong.He apologetically told him that he had misplaced his gun.My friend told him where it was and the Air Guard sheepishly apologised for his carelessness.
The moral of the story is that it is very dangerous to have somebody onboard who has a loaded weapon.He can be over powered by a trained terrorist and basically you have laid grounds for a hijacking in a plate for the terrorist.