Yes, you did see ammonium nitrate in the trunk of the car that tried to get through the Canadian border to bomb LAX. In addition, during the battle of Tora Bora, our troops found al Qaeda records that included the formulation for the OKC bomb identified as such.
I think there were a bunch of propane tanks in the trunk, too. I wonder if Pete King is gonna make all of us pass background checks to buy them in the future?
Anyways, the "formula" for ammonium nitrate is no secret. It's so simple it doesn't need to be written down. The main problem with it as a terrorist weapon is its bulk. Pound for pound its relatively weak and low brisance. It would be the last weapon of choice for any terrorist with access to anything else.