The Bloemfontein tourist centre is a neat, red building overlooking the bus terminal and the football stadium. For visitors to the city it's a fountain of information and advice, but taxi driver William Dube says that for him the innocuous-looking building will always be associated with his torture at the hands of the police.

Dube, a 33-year-old from Pretoria, is awaiting trial in Bloemfontein's Grootvlei prison after being arrested in 2010 on armed robbery charges, by officers of South Africa's organised crime unit. Two weeks later, he says he was taken to an unmarked suite of offices in the tourist centre, where the officers cuffed him to a chair.

"They attached wires to my penis and back from something that looked like an old phone," he said. "Then they wound it up to get power to shock me. It was very, very painful. I even wet myself."

Dube said the officers covered his head with a plastic bag and sealed it with duct tape. "They only remove the plastic when you collapse, then they take it off. While they were suffocating me, they put pepper spray inside the plastic bag and sealed it. They kicked and punched me in the eye and ear. I still can't hear properly."

He says he was taken to the balcony and hung upside down over the edge, an officer holding each leg. That is when he agreed to co-operate with the investigation.

"I was terrified they'd drop me," Dube said. "They told me places to point out, how to make a confession and what to say. I did the pointing out the next day."

Under apartheid, the South African police were notorious for torturing and abusing political detainees, with many unexplained deaths in police cells. But similar brutality in the "new" South African police service has come to the forefront recently, after the massacre of striking mine workers at Marikana and the death in the township of Daveyton of Mido Macia, a Mozambican who was tied to the back of a police van and dragged along the road.

The Independent Complaints Directorate's 2011-12 report records 4,923 complaints received against the police and 720 deaths in police custody or as a result of police action.

"Torture hasn't suddenly reared its ugly head," said Professor Peter Jordi of the Wits Law Clinic at the University of Witwatersrand, who specialises in the subject of torture. "It's never stopped … It was carried out at police stations before and continues today. Previously, it was believed that mostly political detainees were tortured. If you're a criminal arrested for armed robbery today, you face exactly the same fate."

Most incidents of assault and torture are not reported. And if they are, they are unlikely to come to court. Take the allegations made by Dube's co-accused, Mzwandile Khani Khani. Arrested at the same time as Dube, Khani alleges he was brutally assaulted at his home. Two weeks later, he says he was booked out of Grootvlei hospital by organised crime unit members and taken to the tourist centre for a second round of beatings, assault and torture. Like Dube, he says he was cuffed to a chair, had a plastic bag placed over his head and wires attached to his back and penis.

"I was shocked repeatedly for almost four hours in front of a woman officer. There were nine or 10 policemen watching, and kicking me. One of them opened my legs and kicked me in my private parts. I collapsed and fainted. They waited for me to regain consciousness and laughed at me. I heard them say 'hierdie kaffir is baie sterk' [this kaffir is very strong]." Nearly two years later, Khani's hospital records confirm that he still bears injuries.

Khani was one of those to report the matter to Groootvlei prison authorities and to lay charges of assault with intention to do grievous bodily harm against the officers he claims are responsible. He has heard nothing since.

Another co-accused, Lucky Mametsa, said he was also taken to the tourist centre, where his head was repeatedly bashed against a wall to elicit a confession. When he eventually received medical care, he was diagnosed with a broken cheekbone and skull fracture and sent to hospital.

As Mametsa tells it, a scan and x-ray showed the fracture. "The doctor wrote a full-page script but I never received any medicine till today." On his second visit to hospital, Mametsa said he was told he needed an operation, but when he returned for his third appointment his medical records had disappeared. Again he says he was told there was nothing wrong with him.

It is often difficult to corroborate torture allegations because there is no evidence, but when former boxer David Seleke was assaulted outside his home by police the incident was recorded on camera.

Seleke said he was attacked, pepper-sprayed, kicked, beaten and shocked with "something like a cow-prod that the boere [farmers] use for animals" in front of his neighbours. Surveillance cameras that he had installed in his home for his money-lending business recorded the assaults. Unfortunately, the monitor and footage were confiscated by the police.

"Straight after my arrest, I laid charges of assault," he said. "I also complained to the Independent Complaints Directorate. They confirmed the case but said my statement had disappeared. Only a blank docket remained."

Dube, Khani, Mametsa and Seleke are awaiting trial in Grootvlei Prison. Their co-accused, who also say they were mistreated by police, were released on bail last month. To date, all attempts by the men to seek redress have fallen on deaf ears, so they are suing the minister of police, Nathi Mthethwa, for damages.

In addition to laying charges, reporting the matter to the Judicial Inspectorate of Correctional Services and the head of Grootvlei, they have written to the Human Rights Commission, the Independent Complaints Directorate, and Ace Magashula, premier of Free State province.

Police spokesman Brigadier Billy Jones said he was aware of the allegations, which were being investigated. "This office can only confirm that the mentioned accused, who are making these allegations, are currently facing serious charges, namely two of armed robbery and one of burglary at business premises," he said.

The right to be free from torture is enshrined in South Africa's constitution, yet observers say torture is used is part and parcel of criminal investigations.

"Police torture is a daily occurrence in Gauteng where I practise," said Jordi. "I probably handled more than 20 torture cases against the police in Gauteng alone last year."

Jordi believes judges and magistrates are equally to blame. "They deal with individual cases where torture is alleged and ignore the evidence staring them in the face."