I'm sure all these fertilizer places are aware of the possibility of the product they sell being used for explosives.
Not according to the following - "Norman, Oklahoma, feed store owner Dustin Ellison's Sept. 28 encounter with University of Oklahoma suicide bomber Joel Henry Hinrichs was witnessed by a plain-clothes police officer who happened to be in the store at the time"
Which leads back to my previous observation of why there just happened to be an undercover cop in the feed store at that opportune time. And also, why did there just happen to be extra security at that particular football game.
http://tapscottscopydesk.blogspot.com/2005/10/hinrichs-was-known-to-law-enforcement.html