Arafat assassination: some background

A Palestinian physician sent me this:  "As you know, Aljazeera yesterday aired an investigative program about the assassination of Arafat, and what I noticed is something important: two years ago, an officer from the intelligence of the PA defected, and exposed the officials there, one after the other, and his name is Fahmi Shabbanah.  What got my attention is that he said on 17-1-2011 that Arafat was killed by poison and he specified the poison literally, as Polonium, and Aljazeera published the story and here is the link.  So if the officer had said that and specified the poison, why has the PA covered up the story?"