In late 2016, a 47-year-old Uighur employed on a road-building crew in China’s western Xinjiang region started hectoring his co-workers about their behavior.

He warned them against watching porn or swearing, badgered them not to eat food cooked by non-Muslims, smokers or people who drink alcohol and made offensive slurs against the country’s majority Han ethnic group.

In most countries, his remarks would have simply marked him out as a bigot and religious bore. But in China, the state viewed them – and him – far more harshly.

Two years later, the comments would land him in court, and earn him a 10-year sentence for “incitement of ethnic hatred and ethnic discrimination”, according to a leaked summary of his trial.

The case was not exceptional but for the fact that its details have been made public. The individual was not a public figure, and there are no reported consequences of the crime of which he was convicted.

The Uighur-language transcript was not classified, but official secrecy across Xinjiang means court documents are rarely publicly available.

So the details of his mundane offense and sentence provide a rare insight into the nature and extent of a sweeping government crackdown on Uighurs and other ethnic minority groups, which is underway in the region.

China says it is fighting extremism; critics say it is effectively trying to erase Uighurs’ ethnic and religious identity.

The most high-profile features of the government campaign have been internment camps that house at least a million people, held indefinitely for “re-education”.

The inmates of these camps, who make up a majority of Xinjiang’s detained, are people the authorities consider tainted by the “three forces”: terrorism, extremism, and separatism. The courts and formal jail are used only in a minority of cases the state considers more serious.

Yet the trial and sentencing of this single prisoner, whose name the Guardian knows but is not publishing because he could not be reached for comment, is an indication of how low the bar is for criminal offenses.

The trial details were leaked as part of the China Cables, a cache of six official documents shared with, and authenticated through, the International Consortium of Investigative Journalists (ICIJ).

“He incited extremist religious thoughts in his colleagues … [saying things] such as: ‘Do not use dirty words, do not watch porn or you will become a kafir [offensive word for a non-believer],” the charges against him read.

“[He told them]: ‘If you do not pray, you will be in hell and God will not forgive you … You cannot eat food prepared by women who do not pray, you cannot eat food prepared by people who smoke and drink alcohol.”

There is no record that his words led to any form of violence or other criminal offenses, or even if others were spurred on to greater religiosity by his chastisements.

The 10-year sentence appears to have been simply for his proselytizing – and came after his lawyer sought leniency for the first-time offender.

“Due to the defendant’s low legal awareness and education level, he was easily susceptible to being misguided and committing crimes. He’s guilty. This is his first criminal record and I ask the court to deal with him leniently,” his counsel said.

Hundreds of thousands of people are held in camps, presumably for less severe violations, as part of an opaque state-sponsored drive apparently designed to crush all ethnic and religious identity and weaken family ties.

In Xinjiang, behavior that can mark out a person for further investigation – and possible internment – includes simply owning a Qur’an. Mosques have been destroyed, graveyards razed. Children have been separated from their families and held in state-run institutions. At least one area has banned the use of the Uighur language in schools.

The long arm of the state has reached into homes. Han Chinese have been sent to live with Uighur families, calling themselves “relatives” while monitoring every aspect of their hosts’ lives, attending family events such as weddings and funerals, and recording even minor displays of religious sentiment such as refusing to eat pork.

In some cases, the women have reportedly been obliged to share beds with male Han “relatives” assigned to live in their homes. Often these are homes where the men have been detained.

Adrian Zenz, an academic and expert on the camps, says their aim is to effectively erase religious and cultural life. “For the Chinese Communist party, the minorities are an essential aspect of a multiethnic empire that’s being revived,” he said. “So they are not to be killed, but they are to be integrated and assimilated.”

China’s embassy in London said in a statement that documents in the China Cables leak were “pure fabrication and fake news”, denied internment camps existed and said measures taken in Xinjiang were a response to concerns about terrorism.

“Thousands of terrorist incidents happened in Xinjiang between the 1990s and 2016, and thousands of innocent people got killed. So there’s an enormous uproar among the Xinjiang people for the government to take resolute measures to tackle this issue.”

It added “The preventative measures have nothing to do with the eradication of religious groups. Religious freedom is fully respected in Xinjiang.”