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A Russian court is expected to convict a dead man on Thursday, completing the posthumous trial of whistleblowing lawyer Sergei Magnitsky, whose death in detention led to one of the biggest Washington-Moscow rows in years.

The tax evasion case against Magnitsky, who died in pre-trial detention in 2009 after accusing interior ministry officials of corruption, has been slammed by legal experts and Western governments.

Judge Igor Alisov of the Tverskoy District Court in Moscow is expected at noon (0800 GMT) to pronounce the verdict in the case against Magnitsky and his former boss, US-born British citizen William Browder, the head of the Hermitage Capital investment fund who is being tried in absentia.

Magnitsky had accused interior ministry officials of organising a $235-million tax scam, but was then charged with the very crimes he claimed to have uncovered.

He was placed under pre-trial detention in 2008 and died of untreated illnesses less than a year later at the age of 37.

Browder insists Magnitsky was tortured to death with beatings and the refusal of proper medical care.

A onetime supporter of President Vladimir Putin who headed an investment fund that was one of the biggest foreign investors in Russia, Browder has become a vocal critic of Russian authorities and has lobbied Western countries to sanction officials believed to be implicated in Magnitsky's death.

The US earlier this year passed the "Sergei Magnitsky Act" which imposed a visa ban and froze the assets of officials implicated in the lawyer's death.

The legislation infuriated Moscow, which in retaliation passed legislation prohibiting Americans from adopting Russian children.

In April, Russia's justice and interior ministers met with staff included on the list, assuring them that they were in no danger of losing their jobs.

Western states have criticised the trial, with the US State Department saying Russia instead "ought to put its energy into investigating how he died".

Investigators closed the inquiry into the lawyer's death citing "lack of evidence" and last year, a court acquitted of negligence an official from the prison where Magnitsky was held.

Russia's Constitutional Court made it possible to try deceased people under a July 2011 ruling that allowed families of late defendants to push for their exoneration by the courts.

But Magnitsky's family, including his widow and mother, protested when prosecutors re-opened the case against him in August 2011. They have boycotted the trial and have asked the Moscow legal community to do the same.

The trial has gone ahead in a small courtroom since January despite only nominal participation of the two defence lawyers, Nikolai Gerasimov and Kirill Goncharov, who were appointed to the case by the judge at risk of disbarment.

Both have tried to distance themselves from the case, have repeatedly not shown up at the hearings, citing illness or other court engagements, and at one point asked the judge to remove them from the case, a request that was denied.

They were not available for comment.

Speaking to AFP ahead of Wednesday's hearing, Browder said he expected a guilty verdict.

"It will be proof that Putin is ready to misuse the courts and the entire Russian justice system to cover-up serious economic crimes and murder of his top officials."

A guilty verdict against Magnitsky would essentially deny him a chance to be exonerated.

Analysts say that Russia has pressed on with a case against a dead man to make a point.

"This trial is a gesture by Russia. Russia insists that it's not people on the list who are guilty, but Magnitsky and Browder," said Maria Lipman, a political analyst at the Carnegie Center in Moscow.

"Since Browder is not facing the court and Magnitsky is dead, nothing can be proven, but that's not even needed," she said. "It's a gesture of resistance to the Magnitsky Act."

Browder said he would keep up his fight on behalf of the lawyer.

"On the day of Sergei Magnitsky's murder, I made a vow to his memory and his family that I would make sure that the people who killed him face justice, and I will not let this rest until they are all convicted and in jail."