On 26 December 2013, a team of Russian scientists released a report saying they had found no trace of radioactive poisoning—a finding that comes after the French report found traces of the radioactive isotope polonium. Vladimir Uiba, the head of the Federal Medical and Biological Agency, said that Arafat died of natural causes and the agency had no plans to conduct further tests. Unlike the Swiss report, the French and Russian reports were not made public, at the time. The Swiss experts read the French and Russian reports and argued that the radiologic data measured by the other teams support their conclusions of a probable death by polonium poisoning. In March 2015 a French prosecutor closed a 2012 French inquiry, stating that French experts had determined Arafat's death was of natural causes, and that the polonium and lead traces found were environmental.