If they did have that capability they might seize the equipment to maintain the illusion that they did not.
The allied forces did this during the second world war. They could not admit that German encryption had been cracked, so if their only source of knowledge about an event was through breaking of encryption, they would not act on it - even if by doing so, large numbers of civilians would die, because in the long run - far more would be saved by bringing the war to a quicker end.
That's an interesting analogy, but I think that it's not the right one here. Surely the proper analogue would be if the FBI had derived information from their remote infiltration but didn't act on it, rather than if they seized the computer to pretend that they didn't have remote access it?
The allied forces did this during the second world war. They could not admit that German encryption had been cracked, so if their only source of knowledge about an event was through breaking of encryption, they would not act on it - even if by doing so, large numbers of civilians would die, because in the long run - far more would be saved by bringing the war to a quicker end.