The Swiss lab conducting the tests to determine whether late Palestinian leader Yasser Arafat died of polonium poisoning announced on Wednesday that the results will take longer to establish than originally projected.

After Arafat’s body was exhumed in November, Prof. Patrice Mangin, who is in charge of the tests, said that results would be available in three to four months.

However, on Wednesday, a spokesman for the Swiss University Centre of Legal Medicine in Lausanne said that the results would not be available until late spring.

“There are two series of tests that have to be carried out. The first one is complete and we’re going to start the second one, so there won’t be and tangible results until the end of May,” Darcy Christen said.

According to Christen, the results need to be analyzed in detail, and a report must be written and submitted before the results can be made public.

Arafat died in November 2004 in a French military hospital, a month after suddenly falling ill. Palestinian officials claim he was poisoned by Israel, but have not presented evidence. Israel has denied such allegations.

The new probe into his death began in the summer of 2012, after a Swiss lab discovered traces of polonium-210, a deadly radioactive isotope, on clothes said to be his.

The clothes were provided by Arafat’s widow, Suha, and given to the lab by the Arab satellite TV station Al-Jazeera. Separately, Mrs. Arafat asked the French government to investigate, while the Palestinian Authority called in Russian experts.

A leading French doctor who teaches at the Percy hospital where Arafat died told The Times of Israel in November that, based on Arafat’s medical report, there is “absolutely no way” the Palestinian leader was poisoned.

Dr. Roland Masse, a member of the prestigious Académie de Médecine, said the symptoms of polonium poisoning would have been “impossible to miss,” noting that Percy had tested Arafat for radiation poisoning, and revealed that the hospital specializes in the related field of radiation detection. “A lethal level of polonium simply cannot go unnoticed,” he said.

Arafat’s death has remained a mystery for many. While the immediate cause of death was a stroke, the underlying source of an illness he suffered in his final weeks has never been clear, leading to persistent conspiracy theories that he had cancer, AIDS or was poisoned.

Many in the Arab world believe Arafat, the face of the Palestinian independence struggle for four decades, was killed by Israel. Israel vehemently denies the charge.