- French prosecutor says no case to answer regarding Palestinian leader's death
- Al Jazeera investigation in 2012 found evidence of poisoning
- Rival studies carried out by French and Swiss researchers yield different conclusions
- Case centres around polonium isotope that is produced in nuclear reactors
A French prosecutor has said there was no case to answer regarding the death of former Palestinian Authority President Yasser Arafat in 2004.
The request to drop the probe into the leader's death on Tuesday comes two years after French investigators said the level of polonium 210 in Arafat's body was the result of naturally occurring processes involving radon gas, not deliberate poisoning.
Swiss researchers, who carried out an Al Jazeera commissioned analysis of Arafat's possessions at the time of his death and later tissue samples, said the French report found similar levels of polonium but suggested heighened levels "moderately" supported the idea Arafat was poisoned.
Arafat died in Percy military hospital near Paris aged 75 in November 2004 after developing stomach pains while at his headquarters in the Occupied West Bank city of Ramallah.
Speaking to Al Jazeera in late 2013, Francois Bochud, director of the Institute of Radiophysics in Lausanne, said that his team, unlike the French one, took radon measurements from the tomb.
"For us, radon could be ruled out because actually we did measure radon in the tomb before opening it, and the values we found were about the same as we would find in any tomb," Bochud said.
"Actually, it was a bit lower than what we could expect in normal soil. For us, radon is really an explanation that cannot be used."
Al Jazeera's investigation What Killed Arafat? reported how the same Swiss scientists in July 2012 found elevated levels of polonium 210, one of the element's isotopes, in blood, sweat and urine stains on Arafat's clothes.
Suha Arafat, the leader's wife, filed a murder complaint with a French court that same month.
The Swiss found 18 times the expected levels of polonium in Arafat's remains following the exhumation of his body in late 2012.
A Russian study said results of tests on Arafat's tissue and bone samples were inconclusive, but experts questioned those findings.
There has been intense controversy surrounding the different analyses of Arafat's remains and who might have poisoned the Palestinian leader.
Palestinian officials have been conducting their own investigations and have said they will take the case to the International Criminal Court.
Poloniun 210 is a radioactive isotope found naturally in the atmosphere and in soil, but in very small amounts. It is commonly produced in and extracted from nuclear reactors.
Source: Al Jazeera and agencies