Motive? Possibly it is because he was "in the loop" when the CIA informed the committee he once co-chaired that the Middle East threat would shift from the hard target of Washington DC (remember the barricades on Pennsylvania Avenue) to the soft targets in the US. At the top of that list of soft targets was the Oklahoma City Murrah Federal Building.
They also have the problem of an informant telling them that the Murrah building was a target, along with several other buildings.