Mossad did a great job planting data that lead Saddam's son to believe Nidal was an Israeli double agent.
OR ... Saddam saw Nidal as a threat for the 9/11 attack being tied back into Baghdad and Nidal conveniently committed sideways by shooting himself several times. Take your pick. I favor the former, but there is 'stuff' floating about to tilt the latter also. Perhaps the 'Nidal as Israeli double agent' is what has lead the Arab press to accuse Israel of the 9/11 attack, as that would satisfy their irrational hatred of Israel and America.