As in life, anyone in a black suit is a professional. Professionals will shoot even if at gunpoint. They can also see in the dark, because why not?
The professional is an elite variant of the Guard. It can be killed or incapacitated like a normal guard, but it can see as clearly in the dark as in the light and will fire at the player even when held at gunpoint. Professionals will shoot more quickly than guards and enforcers, but do not shoot instantly like the police sniper.
Professionals, like guards, will react to lights being switched off: they will begin a patrol if the lights are switched twice, and will try to switch on the lights in a dark room if there is a light switch.
Professionals can see Conway through other enemies.
The best tactic for taking down a Professional is hanging over a doorway and pouncing on them as they go through the door, as the vision cone is the same as other guards.