According to the BBC report here http://news.bbc.co.uk/1/hi/world/americas/3624049.stm:

Mr Ashcroft expressed sorrow and anger over the events of 11 September 2001, and said he would have deployed all available resources to prevent the attacks had he known they were coming.

But he added: "The simple fact of September 11 is this, we did not know an attack was coming because for nearly a decade, our government had blinded itself to its enemies. However, on July 26, 2001, CBS News reported that John Ashcroft had stopped on flying commercial airlines due a threat assessment.

The CBS report is still available here: http://www.cbsnews.com/stories/2001/07/26/national/main303601.shtml

There's a local copy of the text of that report here.