The brutal rape and death of a Russian man in police custody has prompted scores of other hesitant victims to come forward and denounce brutality they had been to frightened to report before.

In the central Russian city of Kazan where the abuse took place, around 40 people shuffled on the steps of the regional Investigative Committee last week, waiting to give a formal account of their experiences of police torture.

A team of senior investigators had come from Moscow, around 800 kilometres (500 miles) away, to investigate the death of Sergei Nazarov, 52, who was raped with a champagne bottle while police questioned him on suspicion of theft.

Investigators are now looking into at least three incidents at the same police station, Dalny, and have detained seven police officers based there.

One of the victims, IT specialist Oskar Krylov, 22, said he felt lucky to be alive after being sexually assaulted at the Dalny station while in custody on suspicion of theft in October last year.

When he refused to confess, three policemen including the head of the station's criminal investigation squad, Ainur Rakhmatullin, raped him first with a pen and then with a bottle, he said.

"I shouted 'Help!' and 'Let me go, I will sign anything,' but Rakhmatullin just told me: 'You should have signed when we were treating you nicely. Now we are going to screw you all night.'"

"Now after what has happened with Nazarov, I tell myself that I'm alive and in good health - that I was lucky," he said.

While police brutality at Dalny has been widely covered in the media, the regional police insists that these were isolated incidents, not system-wide abuses - a view dismissed by rights campaigners.

"People should trust the police," Kazan's police chief, Rustem Kadyrov, said.

"I don't think it's fair to draw broad conclusions from a single shameful case."

Those waiting outside the regional Investigative Committee did not share his view, recounting story after story of how their sons or brothers had been victims of police abuse.

Tasima Minimulovna, a woman in her 50s, wept as she described how her son, Airat, was beaten for days at another Kazan police station until he confessed to a murder and attacks on taxi drivers.

Although he subsequently retracted his confession, he was still being held in pre-trial detention, she said.

"The police only work for their own interests. They don't give a damn about anything, and they would use any method to put my son in jail," she said.

The director of the Kazan Rights Centre, Igor Sholokhov, this week passed 17 files to the prosecutors alleging police brutality. Five of the victims had died in detention. Yet he said the region was not exceptional.

"Tatarstan is no better or worse than other regions," said Sholokhov, a former prisoner governor who now spends his time exposing police violence.

He blamed a system in which police officers' pay and perks depend on whether they reach targets on recording and solving crimes - and no one asks too many questions about their methods.

"This is how the police get bonuses and promotion and other perks and how they avoid punishment for doing their work badly," he said.

"To get good reports, they use torture," he added - and almost anyone could be a victim.

"Your social position or level of education makes little difference."

The scandal in Tatarstan has prompted rights groups to publicise numerous similar cases across Russia.

The Memorial rights group raised the case of a young man from the North Caucasus who was detained in the Moscow region this month and was beaten and had his nails ripped out in an attempt to make him testify against a friend.

Outgoing Russian President Dmitry Medvedev made police reforms one of his key policies, but the public's view is that he has achieved little.

A recent survey by Levada independent polling centre found that 75 per cent of Russians saw no improvement and 14 per cent thought the situation had got worse.