It was a scene that riveted the world for weeks: The ailing Yasser Arafat, first besieged by Israeli tanks in his Ramallah compound, then shuttled to Paris, where he spent his final days undergoing a barrage of medical tests in a French military hospital.

Eight years after his death, it remains a mystery exactly what killed the longtime Palestinian leader. Tests conducted in Paris found no obvious traces of poison in Arafat’s system. Rumors abound about what might have killed him – cancer, cirrhosis of the liver, even allegations that he was infected with HIV.

A nine-month investigation by Al Jazeera has revealed that none of those rumors were true: Arafat was in good health until he suddenly fell ill on October 12, 2004.

Tests have revealed that Arafat’s final personal belongings – his clothes, his toothbrush, even his iconic kaffiyeh – contained abnormal levels of polonium, a rare, highly radioactive element. Those personal effects, which were analysed at the Institut de Radiophysique in Lausanne, Switzerland, were variously stained with Arafat’s blood, sweat, saliva and urine. The tests carried out on those samples suggested that there was a high level of polonium inside his body when he died.

The findings have led Suha Arafat, his widow, to ask the Palestinian Authority to exhume her late husband’s body from its grave in Ramallah.

But a conclusive finding that Arafat was poisoned with polonium would not explain who killed him. It is a difficult element to produce, though – it requires a nuclear reactor – and the signature of the polonium in Arafat’s bones could provide some insight about its origin.

Al Jazeera Investigates: What Killed Arafat can be seen on Al Jazeera English at the following times GMT: Tuesday, July 3: 2000; Wednesday, July 4: 1200; Thursday, July 5: 0100; Friday, July 6: 0600; Saturday, July 7: 2000; Sunday, July 8: 1200; Monday, July 9: 0100; Tuesday, July 10: 0600. Click here for more on the special investigation