Russian investigators on Thursday charged four policemen with asphyxiating a witness using a gas mask as the force reels from a series of torture allegations. The four officers in the southern Siberian city of Novokuznetsk are accused of deliberately causing severe bodily harm and causing the death of a 31-year-old man, the Investigative Committee said in a statement. \"The policemen checking the man\'s involvement in a crime, put a gas mask on him and beat him up to try to get evidence. He died from his injuries,\" the investigators said. They added that police attempted to cover up the death in September last year as suicide, but pathologists who examined the body found the man had died from asphyxiation. In a separate case on Thursday three policemen were arrested and charged with brutally beating a 20-year-old woman over several hours in the city of Orenburg in the Urals mountains. Reports of brutal treatment of suspects in police stations have multiplied after a scandal in the central Russian city of Kazan, where a man died in custody this month after being beaten and raped with a champagne bottle. While officials dismissed the torture as an isolated incident, rights activists and victims have spoken out, painting a bleak picture of systematic police violence that goes largely unpunished. On Thursday, investigators accused one of the officers at the centre of the Kazan scandal of beating and attempting to rape another suspect with a pencil in February last year. He was also accused of slapping another man in the face in an attempt to make him confess to stealing a cell phone. In the republic of Bashkortostan, an investigation was opened after a 16-year-old and his 22-year-old friend claimed they were beaten by police in March. In the same region, the Committee Against Torture group said it received testimonies from two individuals who claimed to have been tortured in December and February respectively. They were beaten, asphyxiated and one of them, who had to be hospitalised for 32 days, said he was sodomised with an iron rod. Their tormentors reportedly went by nicknames such as \'Gestapo\' and \'SS\'. Russia\'s interior minister Rashid Nurgaliyev has held public meetings to address violence in the police, but has denied the problem is systemic. This week the minister outraged the public by suggesting that artists and cultural figures should teach police officers to \"find beauty in everyday life\" and create \"relaxing conditions\". Russia\'s President Dmitry Medvedev last year backed reforms that included renaming the police service and forcing officers to reapply for their jobs. However, rights activists and lawyers have said the reform was mostly window-dressing that did little to eradicate corruption or make violent officers accountable for their actions.