The ambush by the Chechens appeared highly successful. As a unit of 98 Russian soldiers entered Grozny on board nine trucks, they came under fire from machine-guns and grenade launchers.

By the time the slaughter ended four hours later, 22 Russians were dead and 31 wounded. A Chechen commander said he had made the attack, and the Kremlin was specific: the Chechen guerrillas had caught by surprise the interior ministry troops, known as Omon in Russia, newly arrived from the town of Sergiyev Posad near Moscow. The attackers got away because they had booby-trapped their escape route.

An interior ministry general gave a similar account of the devastating ambush to the Russian parliament.

None of it was true. In fact, the Russian soldiers fell victim to "friendly fire". The accounts of the Chechen attack two years ago were a cover-up.

The men from Sergiyev Posad were killed by Russian troops who believed they were shooting at Chechen guerrillas in disguise.

Three senior Russian officers go on trial this week accused of negligence leading to the worst Russian losses from friendly fire since the beginning of the second Chechen war in 1999. Among the accused is Major-General Boris Fadeyev, now the head of the Moscow region traffic police, who was then a commander in the Russian military headquarters for Chechnya. Also on trial are Major Igor Tikhonov, the commander of the Omon unit that shot its comrades, and Colonel Mikhail Levchenko, an interior ministry official in Chechnya.

Information from the Russian prosecutor's office and leaks in the Russian press say local police and an Omon unit from Podolsk in the Moscow region did not know about the arrival of the soldiers from Sergiyev Posad. They also had information that guerrillas wearing police uniforms might try to infiltrate Grozny, the Chechen capital, and were waiting for them. The cover-up underlined the difference between the war as reported in the Russian media and events on the ground.

Although the military insists they are now in the last stages of a mopping-up operation, Chechen guerrillas appear able to enter at will towns long under Russian control.