OU engineering student Joel Henry Hinrichs III tried to buy ammonium nitrate fertilizer from Ellison Feed and Seed in east Norman.
http://www.normantranscript.com/cnhi/thenormantranscript/homepage/local_story_277224148.html?keyword=leadpicturestory
This is hearsay, but Ann Coulter was reported to have casually mentioned on TV that a dirty bomb was already attempted. Maybe someone can verify that she said this or else clarify it. My memory is pretty good but not perfect.
I know from a bomb disposal officer that many bombs were set during the Viet Nam war and neutralized with no publicity.