How do I save commisioner gordon without being detected?

If you are on the Xbox one I'll give you a detailed description of how I did it... So first you must open the vent at the end there should be a danger do not whether sign outside behinds the brick wall, then take out the man closest with the silent takedown or Y button then continue into the next vent, then the one in front of the next vent I always open the vents before I start, and I always use the vent on the side of him which is next after then one behind him then take him out...rushing back into the vents as they cannot see you there... Then when one henchman is below and the one up top is not able to see him you can silently go down from that same cent use Silent takedown then hurry back up to he vent,now the last one is tricky it may seem easy but you must wait till his back is turned then take him out but I am personally never able to get there fast enough and he turns around, but the rest will for sure work if you do it right!