Russia has been accused by a leading human rights group of a cover-up of one of the worst unsolved crimes of the Chechen war, the discovery earlier this year of 51 bodies dumped outside its main military headquarters.
A report by the US-based Human Rights Watch alleging lapses by investigators has been released to coincide with today's EU-Russia summit in Moscow.
"This is powerful evidence of some of the worst abuses in Chechnya," said Ms Holly Cartner, a director of Human Rights Watch.
"This week is a key opportunity for leaders to get some answers from the Russian government."
The mass grave was discovered on February 24th, when the bodies, many showing signs of torture, were discovered dumped among a group of former holiday homes about one kilometre from the military headquarters at Khankala, outside the capital, Grozny.
At the time, human rights groups demanded an investigation into how much the high command knew about the bodies, and justice officials began an examination.
The Russian human rights group, Memorial, gained access to a temporary morgue.
It produced photographs showing evidence of torture on the bodies, some of which had been scalped or had fingers or ears missing.
Some also had broken limbs, and many had their hands bound behind their backs with rope or wire, and had been shot through the head at close range.
But two weeks after the discovery, Russia buried 34 of the bodies, along with the clothing, bullets and other evidence needed by investigators, Human Rights Watch said.
Most damning of all, it said that 16 of the 19 bodies that were identified, all of them Chechen civilians, were last seen in the custody of security forces.
Nobody has yet been charged with the killings, and Russia has yet to respond to the report.
Other criticisms made by the report include the lack of resources for analysis provided to the civilian examiner.
The equipment provided was limited to a scalpel and rubber gloves.
Russia is likely to face criticism today when President Vladimir Putin meets the EU foreign policy leader, Mr Javier Solana, and the President of the European Commission, Mr Romano Prodi, in the Kremlin.
Last month the EU tabled a motion, approved by the UN Human Rights Commission, condemning Russia for its record of investigating reports of atrocities in the province.