(JTA) — Palestinian investigators said that Israel is the “only suspect” in the death of Yasser Arafat, after laboratory tests suggested the Palestinian leader died from poisoning.

“We say that Israel is the prime and only suspect in the case of Yasser Arafat’s assassination, and we will continue to carry out a thorough investigation to find out and confirm all the details and all elements of the case,” Palestinian inquiry chief Tawfiq Tirawi told a news conference in the West Bank city of Ramallah, the French news agency AFP reported Friday.

Tirawi said the Palestinian inquiry had studied the findings of Swiss scientists, released Wednesday, which “moderately” supported the notion that Arafat had been poisoned with polonium, a radioactive substance.

Palestinian officials on Thursday demanded an international inquiry into Arafat’s “killing.”

Wasel Abu Yusef, a senior Palestine Liberation Organisation official, said polonium ”is owned by states, not people, meaning that the crime was committed by a state.”

Speaking to reporters in Lausanne Thursday, the Swiss team said the test results neither confirmed nor counted out that polonium was the actual source of his death, although they provided “moderate” backing for the idea he was poisoned.

They said the quantity of the deadly substance found on his remains pointed to the involvement of a third party.

“We can’t say that polonium was the source of his death… nor can we rule it out,” said Professor Francois Bochud of the Lausanne Institute of Applied Radiophysics.

Arafat died in France on November 11, 2004 at the age of 75 after falling sick a month earlier, but doctors were unable to specify the cause of death. His remains were exhumed last year.