The Swiss special prosecutor spearheading a high-stakes investigation into corruption between Fifa president Gianni Infantino and Switzerland’s former top legal official has been ordered to step down.

In a significant legal victory for the governing body of world football, Switzerland’s Federal Criminal Court ruled on Wednesday that a probe opened last year into Infantino and Swiss attorney-general Michael Lauber was tainted by bias.

The judgment is a major setback for Swiss law enforcement in its labyrinthine legal efforts against Fifa, which has its global headquarters in Zurich.

Investigations of wrongdoing at the football body have dragged on for years in the wealthy and secretive alpine country, with few successful prosecutions to date.

Last year events took a dramatic turn when a case was opened to investigate whether Lauber, who as attorney-general since 2012 built much of his career around sensational legal challenges to Fifa, had himself been compromised in his dealings with the body.

Stefan Keller, a prominent jurist, was appointed as special prosecutor by Swiss parliamentarians, with authority independent of the attorney- general’s office, to investigate Infantino and Lauber. Lauber’s immunity from prosecution was also lifted.

The probe was triggered by documents leaked in 2019, that revealed off-the-books meetings held in hotels between Infantino and Lauber, in which highly sensitive ongoing legal matters pertaining to Fifa were discussed.

Infantino said he had met Lauber to emphasise Fifa’s willingness to co-operate fully in ongoing investigations.

Controversy over the meetings was nevertheless stoked by apparently contradictory recollections of what had taken place, and when.

Lauber was found by the Federal Administrative Court to have “intentionally” lied and made “implausible” statements about the meetings.

The attorney-general was subsequently forced to resign, as Switzerland’s ordinarily quiescent parliament prepared to impeach him.

The ongoing investigation into the matter has now been brought to an abrupt halt, however, by the ruling to force Keller to step down. It is unclear who will succeed him, or if the probe will continue.

The federal criminal court ruled that Keller’s work was prejudiced, as indicated by statements he had given to the media.

“Taken as a whole, the impression arises that the [special prosecutor’s] aim with media releases was not an objective communication of important interim steps . . . but rather, biased reporting . . . Thus it can no longer be assumed without doubt that the [special prosecutor] is impartial towards [Infantino],” it said in a judgment on Wednesday.

In a statement, Fifa said it welcomed the court’s decision to remove Keller.

“The [court] emphatically declared that the bias of Keller, as demonstrated by his various media releases, repeated procedural errors, and consistent denial of rights, could not guarantee a fair process,” it said.

“By attempting to look into matters that had nothing to do with his mandate and then publicly raising his own personal suspicions about them without any objective justification, Keller had clearly violated the presumption of innocence and damaged the standing of the Fifa president, contrary to his personal rights protected under the law.”

The supervisory body responsible for Keller’s appointment, AB-BA, said it had taken note of the federal criminal court’s decision.

“We will exchange views concerning the decision with the [parliamentary] Swiss Judicial Committee,” AB-BA told the Financial Times.

The committee is due to convene on May 19.

Lauber could not be reached for comment.

He has repeatedly denied any wrongdoing in his dealings with Infantino.

In a statement issued at the time of his resignation, he said that while he rejected any suggestion of impropriety on his part, trust in his office was essential and he wished to step back “in the interests of the institution.”