Why the FBI etc removed the actual cameras

Sorry if this has been asked already, have tried a search...

Just wondering why the authorities had to remove the actual cameras. e.g Pentagon, Hotel, Citigo petrol Station.

As the cameras don't hold the recordings. These will be on a central recorder, Harddrive, VHS tape or CD/DVD recording.

Any ideas would be great?

Maybe the idea was that they could deny cameras having ever been there, thus no recordings of the impact from those sites. Did you read Jack Tripper's account from going to the Pentagon and taking photos of where the cameras used to be, and talking to the relevant guys?