A sniper shot notorious Russian criminal boss Aslan Usoyan, known as Grandpa Hassan, from a sixth-floor stairwell in a neighbouring building, investigators into the murder said Thursday. A bystander caught in the crossfire lay in hospital in a critical condition as investigators pieced together Usoyan\'s dramatic last moments. A sniper shot at Usoyan as he entered a restaurant on a central Moscow street Wednesday accompanied by two bodyguards, wounding him in the neck, investigators said in a statement. One of the bodyguards fired back at the sniper with a pistol. They pushed Usoyan into the restaurant but the sniper fired another five shots through the closed door, seriously wounding a female member of staff.  \"Investigators believe that the shot was fired from a stairwell between the fifth and sixth floors\" of a neighbouring building, the Investigative Committee said. This was where investigators found a folding chair, a piece of cloth and six cartridge cases. The sniper is thought to have fired an AS VAL machine gun, which is used by Russian special forces and can pierce a 6-mm sheet of steel.\"Aslan Usoyan was shot by a professional hitman who hit his target accurately at a distance of 100-120 metres,\" a law enforcement source told the ITAR-TASS news agency. The 30-year-old woman was shot in the hip and chest, investigators said. She was in intensive care Thursday after surgery, having lost 4.5 litres of blood, RIA Novosti reported, citing a medical source. Usoyan\'s bodyguards did not wait for an ambulance but gave him first aid and drove him to the Botkinskaya hospital, where he died, investigators said. Investigators are doing tests on fingerprints and traces left at the scene and examining security camera footage from nearby buildings, ITAR-TASS reported, citing a source in the investigation. The Life News website posted investigators\' footage of the open window in the stairwell used by the sniper on a street in one of central Moscow\'s swankiest residential areas. A law enforcement source told Life News that a resident recalled to men who had asked to enter the building in search of a non-existent organisation and then \"walked up to the landing between the 5th and 6th floors and looked out of the window.\" Two residents said they received mysterious phone calls asking them whether they were interested in selling or renting their apartments, the source told Life News. Usoyan lunched almost daily at the same restaurant serving food from the Caucasus region, Kommersant business daily wrote, adding that the sniper picked one of his few vulnerable moments. He always travelled in a convoy of four armoured cars accompanied by several dozen guards. The apparent contract killing reflects a turf war between two clans but could be one of the last such killings as the old-style mafia gives way to a new generation of criminal organisations embedded inside the police and local authorities, criminologist Yakov Gilinsky told Kommersant FM radio station. \"I think this is one of the last great showdowns.\" Usoyan was an ethnic Yezidi Kurd born in Georgia who served numerous sentences in Soviet times for robbery, \"speculating\" and disobeying police. He walked out of jail for the last time in 1991, Kommersant business daily reported. From the 1960s he headed a criminal group that organised black-market business across the country. He was one of the criminals known as a \"thief in the law,\" who followed strict gangland honour codes. Today \"his criminal gang still remains the most powerful in the post-Soviet region,\" wrote Kommersant business daily, citing police sources as saying his nephew was likely to take over the reins. He survived at least four earlier assassination attempts, Russian television reported. Most recently, in 2010, he was shot three times in the stomach with a Kalashnikov but survived. In a similar assassination, his ally Vyacheslav Ivankov, known as Yaponchik, or Little Japanese, was shot outside a Thai restaurant in Moscow in 2009. He died months later from his wounds.