Comment: Perhaps it's because Mossad would expose the FBI's role in the..

... Oklahoma City bombing. Pots don't like to call the kettles black.

There are elements in both organizations who are involved in terrorism. I would have to assume it's the people at the top who would stop any investigation that would lead to the truth.

It's not the first time investigators were stopped from pursuing "terrorist".

Case in point...
FBI agents Robert Wright and John Vincent told ABCNEWS the FBI stopped them from pursuing a criminal investigation of terror suspects.

http://911review.org/Reports/FBI_wright.html