Gazing uncertainly past the camera, she recounted her sins in a soft, hesitant voice. An orange prison jacket had replaced her designer clothing. Though her case might be more salacious than usual, the overall effect was familiar: this was the latest videoed confession aired by China's state broadcaster.

Guo Meimei is not a convicted criminal. But if anyone doubted the merits of the 23-year-old's detention, there she was in person, confirming her involvement in illegal gambling and commenting on the numerous men who had offered her large sums for sex.

Over the last year, China has paraded a series of high-profile detainees on television, ranging from 70-year-old journalist Gao Yu to Peter Humphrey, the British investigator jailed last week for illegally obtaining private information.

Many have confessed their guilt to the nation before they have been indicted, let alone tried and convicted. Most have been held for weeks before their admissions were aired.

"Televised confessions serve political needs," said Wang Qinglei, who said he was fired by the state broadcaster CCTV after publicly criticising such confessions.

"People who have been confessing on the state broadcaster have not done any serious crimes. We should ask ourselves why their confessions should take up the state broadcaster's precious airtime."

While detainees have been interviewed on television before, their confessions have usually been aired after court cases concluded, he said. Others said such videos had involved regular criminal cases rather than those with a political dimension.

Chinese-American businessman Charles Xue was detained for hiring a prostitute, but also apologised for "irresponsible" online posts in his televised statement. He was an outspoken social commentator with 12 million microblog followers.

Gao, a prominent advocate of press freedom, expressed "deep remorse" for obtaining a secret document and sending it to an overseas website. Sympathisers believe the allegations may relate to document No 9, an internal party edict warning of the dangers posed to China by the spread of ideas such as universal values and western constitutional democracy.

Confessions have long played a central role in Chinese criminal justice, said Glenn Tiffert, who researches Chinese criminal justice in the 20th century at the University of California, Berkeley.

But human rights groups have warned that coercion is widespread, though China has vowed to crack down on forced confessions.

For the party, confessions are not only about proving the case against the suspect, but also reforming the individual's thought and setting an example to others. "These are model performances meant to publicly abase high-profile figures, demonstrate their submission to party and state authority, communicate new standards of behaviour and warn others to conform, and reclaim popular legitimacy," said Tiffert. He drew a comparison with the pre-trial publication of confessions in newspapers in earlier anti-corruption drives such as the 1951 "three-anti" campaign.

Guo's cowed demeanour was in striking contrast with her reputation for flaunting designer wares and bragging about her wealth. She had parlayed an internet scandal into minor celebrity, having initially gaining notoriety for posting pictures of herself living lavishly while falsely claiming she was a senior figure with the Chinese Red Cross. Donations to the charity plummeted because people saw her as evidence of wrongdoing. "Because of my own vanity, I made a huge mistake," she said of that incident.

Chen Li, of the political and judiciary commission, said: "Guo Meimei is a representative for many social problems … Her sugar daddy, showing off her wealth, charity problems, gambling and prostitution are all very serious social issues. We should really think about those issues reflected by Guo Meimei."

Though the titillating details of her case drew plenty of attention, they did not prevent scepticism. Some viewers suggested the authorities were using Guo to divert attention from news stories including the fatal explosion at a factory the previous day that claimed more than 70 lives.

Whether agreeing to record confessions has won suspects more lenient treatment is unclear. Some have subsequently been released, but others are still being held months later or face trial.

A lawyer, Zhou Ze, said his journalist client, Liu Hu, had a simple reason for refusing to record a confession: "He did not believe he was guilty." Liu was released on bail early this month, having been held for a year on suspicion of defamation after accusing a senior official of neglecting his duties.

Zhou said the televised statements were demeaning to individual dignity as well as raising concerns about due process.

"If it is the media [that] decides to publicise televised confessions before a proper trial, it is a violation of media ethics. If the authorities are behind these confessions, it is a severe violation of the basic principle of presumption of innocence," he added.

* Additional research by Luna Lin