Only the first spy (or Security Bureau) contributes to catching spies in the tile--so if you had 50+ spies in every city and every tile, you were wasting 49 of them. I think I remember you posting about that game.
If one of your spies (or security bureau) detects an enemy spy, it automatically kills it so you don't actually see it. I think the OP wants a unit that can let you see the enemy spy and then choose to kill it. I have no idea how to implement such a thing.