Former French President Jacques Chirac knows what killed Yasser Arafat and should make it public, an ex-Arafat aide said Saturday, reiterating that he believes his boss was poisoned by Israel. French doctors who treated Arafat said he died of a massive stroke after suffering intestinal inflammation, jaundice and a blood condition known as disseminated intravascular coagulation, or DIC. Bassam Abu Sharif, a former Arafat aide, told reporters Saturday - on what would have been Arafat's 78th birthday - that Chirac and Arafat's French doctors know the real cause of death but decided to withhold it from the public for fear of further destabilizing the Middle East. Abu Sharif said he believes Israel killed Arafat with a substance that destroys red blood cells. Asked for proof, he said he would reveal his sources if Chirac publicly denies his allegations.