When you read all of this, you'll realize (feedback if you don't and it's only me), Clarke is good at sugarcoating and revising history, especially when it contradicts what was previously said; and O'Neill was in fear of his life... not from the towers, i'm sure he knew when he went there they would be hit and the only way he could do something is to do the best he could being there, but from those he worked with and under... he knew too much.
John O'Neill was an F.B.I. agent with an obsession: the growing threat of Al Qaeda.
by LAWRENCE WRIGHT
http://www.newyorker.com/fact/content/articles/020114fa_FACT1
O'Neill was right about a lot; including that AQ cells were established here.