Schwazer was banned for eight years in 2016 for a second doping offence, having previously served a three-and-a-half year suspension for testing positive for erythropoietin before the London 2012 Olympics.

The Italian has not disputed results of that first test.

He did claim he was a victim of foul play related to his second ban, which was handed to him following a sample from January 1 in 2016.

It had initially given negative results, but a new analysis revealed traces of steroids.

A court in Bolzano last February dismissed a criminal doping case against Schwazer, with the investigating judge making a series of accusations against World Athletics, the anti-doping laboratory in Cologne and WADA.

The WADA said Judge Walter Pelino had argued the sample had been manipulated, based on the contention that the concentration of DNA in the sample was "too elevated to be physiological".

Judge Pelino concluded that the sample must have been 'concentrated' by heating in order to increase the likelihood that it would test positive, with the consequence that the DNA levels increased.

It was claimed an unidentified person obtained a third party’s sample that contained synthetic testosterone, exposed it to ultra violet rays to remove all traces of that third party’s DNA, mixed it with the sample, then heated the combined sample to increase the concentration of synthetic testosterone.

The Swiss Federal Tribunal rejected a petition from Schwazer to overturn his eight-year ban last May.

The WADA and the Athletics Integrity Unit (AIU) commissioned the Forensic Genetics Unit in Lausanne to conduct a study following Judge Pelino's verdict.

The study involved the analysis of the urinary DNA concentrations of 100 samples from male endurance athletes.

"The results demonstrate conclusively that the DNA concentration in the sample is well within the physiological range," the WADA said.

"Indeed, much higher values were obtained, even after years of storage, and approximately 20 per cent of the samples had DNA concentrations greater than the highest concentration detected in the sample.

"Therefore, the whole basis for the manipulation scenario (i.e. the supposedly non-physiological concentration of DNA in the sample) is wrong."

The organisation said it sought the opinion of international anti-doping scientist Professor Martial Saugy on the plausibility of the manipulation scenario.

"The very clear opinion of Professor Saugy is that the manipulation scenario devised by Judge Pelino is wholly implausible," the WADA said.

"First, it would make no scientific sense to heat (or concentrate) the mixture of urines as this would not increase the likelihood of the sample testing positive.

"Second, there is no indication of manipulation in the analytical data; according to Professor Saugy, it would have been close to impossible to manipulate the sample in the manner described without leaving analytical traces.

"Third, this would have required access to Mr Schwazer’s steroid profile, which the Cologne laboratory did not have."

The WADA had previously said the judgement reached by Judge Pelino had an obvious "lack of fairness and due process".

The organisation said it was neither involved in the collection, the Cologne laboratory’s initial testing nor the subsequent retesting of the sample, while saying the judge had opted to disregard evidence when making his decision.

WADA director general Olivier Niggli said the study and opinion of Professor Saugy confirms the organisation’s position.

"It has always been WADA’s contention that the judge’s manipulation theory was not supported by the facts," Niggli said.

"The results of the DNA study and Professor Saugy’s review of the evidence confirm our position and fully refute Judge Pelino’s theory, which was predicated on a series of incorrect assumptions."

Schwazer was stripped of a World Race Walking Team Championships title won in Rome in 2016 as a result of the second anti-doping violation.

The Italian won gold in the men’s 50 kilometre race walk event at the Beijing 2008 Olympics, but his career has been the subject of significant controversy.

The full WADA and AIU position can be viewed here Schwazer JOINT STATEMENT EN_0.pdf