Flight crew -- at least one of them on board -- know who the FAMs are on their flight. Traditionally they have also been informed about the other armed LEOs or authorized cabin gun-bearing passengers on their flights.

I am speaking of US airlines here. Foreign airlines with armed guards don't have all the same practices, even as many of the practices are very much akin.

Are you trying to write a sequel to a movie or a new movie plot? It's already been considered.