RIYADH (NYTIMES) - Businessmen once considered giants of the Saudi economy now wear ankle bracelets that track them.

Princes who led military forces and appeared in glossy magazines are monitored by guards they do not command.

Families who flew on private jets cannot gain access to their bank accounts. Even wives and children have been forbidden to travel.

In November, the Saudi government locked up hundreds of influential businessmen - many of them members of the royal family - in the Riyadh Ritz-Carlton in what it called an anti-corruption campaign.

Most have since been released but they are hardly free.

Instead, this large sector of Saudi Arabia's movers and shakers are living in fear and uncertainty.

During months of captivity, many were subject to coercion and physical abuse, witnesses said. In the early days of the crackdown, at least 17 detainees were hospitalised for physical abuse and one died in custody with a neck that appeared twisted, a badly swollen body and other signs of abuse, according to a person who saw the body.

In an email to The New York Times on Sunday (March 11), the government denied accusations of physical abuse as "absolutely untrue".

To leave the Ritz, many detainees not only surrendered huge sums of money, but also signed over to the government control of precious real estate and shares of their companies - all outside any clear legal process.

The government has yet to actually seize many of the assets, leaving the former detainees and their families in limbo.

One former detainee, forced to wear a tracking device, has sunk into depression as his business collapses.

"We signed away everything," a relative of his said. "Even the house I am in, I am not sure if it is still mine."

As the architect of the crackdown, Crown Prince Mohammed bin Salman, prepares to travel to the United States this month to court American investment, Saudi officials are spotlighting his reforms: his promise to let women drive, his plans to expand entertainment opportunities and his moves to encourage foreign investment.

They have denied any allegations of abuse and have portrayed the Ritz episode as an orderly legal process that has wound down.

But extensive interviews with Saudi officials, members of the royal family, and relatives, advisers and associates of the detainees revealed a murkier, coercive operation, marked by cases of physical abuse, which transferred billions of dollars in private wealth to the crown prince's control.

Corruption has long been endemic in Saudi Arabia, and many of the detainees were widely assumed to have stolen from state coffers.

But the government, citing privacy laws, has refused to specify the charges against individuals and, even after they were released, to clarify who was found guilty or innocent, making it impossible to know how much the process was driven by score-settling.

Part of the campaign appears to be driven by a family feud, as Crown Prince Mohammed presses the children of King Abdullah, the monarch who died in 2015, to give back billions of dollars that they consider their inheritance, according to three associates of the Abdullah family.

And although the government said the campaign would increase transparency, it has been conducted in secret, with transactions carried out in ways that avoid public disclosure, and with travel bans and fear of reprisals preventing detainees from speaking freely.

Most people interviewed for this article spoke on the condition of anonymity to avoid the risk of appearing to criticise Crown Prince Mohammed.

The government said in its email that "the investigations, led by the Attorney General, were conducted in full accordance to Saudi laws. All those under investigation had full access to legal counsel in addition to medical care to address pre-existing, chronic conditions".

In a separate statement on Sunday announcing new anti-corruption departments in the attorney general's office, the government said King Salman and Crown Prince Mohammed "are keen to eradicate corruption with utmost force and transparency".

Before dawn on Nov 4, Prince Alwaleed bin Talal, the kingdom's most famous investor and one of the world's richest men, was asleep at a desert camp when he was summoned by the royal court to see King Salman, according to two associates of his family. He returned to Riyadh, where his guards were dismissed, his phones taken from him and he was locked in the Ritz.

Over the next 24 hours, similar calls lured in more than 200 people, including some of the kingdom's wealthiest and most powerful men. They included Prince Mutaib bin Abdullah, a son of King Abdullah and head of one of the country's three main security services; Fawaz Alhokair, who owned the kingdom's franchises of Zara, the Gap and dozens of other stores; Salah Kamel, an elderly businessman from the Red Sea port city of Jiddah; and many other princes, businessmen and former government officials.

Most ended up in the Ritz, where they could watch television and order room service but had no internet or phones.

Outside, their relatives panicked, and managers of their far-flung businesses drew up contingency plans to keep operations running, unsure of how long their bosses would be gone.

Eventually, the detainees were allowed to reassure their families through short, monitored calls.

Many were prevented from contacting their lawyers, but Prince Alwaleed spoke weekly with some of his managers, his associates said. He remained out of public sight until January, when the royal court allowed a journalist from Reuters to interview him in the Ritz to counter a BBC report that he was being kept in a cell-like room.

"Rest assured that this is a clean operation that we have," the prince told Reuters, having visibly lost weight and grown a beard. "There is a misunderstanding and it is being cleared."

Within a few hours, he was released, but even close associates say they do not know what agreement he made with the government.

In the early days of the Ritz detentions, as many as 17 detainees required medical treatment for abuse by their captors, according to a doctor and a US official.

Relatives of some of the detainees said they were deprived of sleep, roughed up and interrogated with their heads covered while the government pressured them to sign over large assets.

Evidence of such abuse has been slow to emerge, but officials from two Western governments said they deemed the reports credible.

One case involved a Saudi military officer who died in custody.

One person who saw the corpse of the officer, Major-General Ali al-Qahtani, said his neck was twisted as if it had been broken, and that his body was badly bruised and distended. His skin showed other signs of physical abuse, the person said.

A doctor and two other people briefed on the condition of the body said it had burn marks.

In the emailed response to questions about al-Qahtani, an official of the Saudi Embassy in Washington said: "All allegations of abuse and torture of those investigated during the anti-corruption proceedings are absolutely untrue."

Al-Qahtani, an officer in the Saudi National Guard who was believed to be about 60, was not wealthy himself, so his value as a major anti-corruption target is questionable. But he was a top aide to Prince Turki bin Abdullah, a son of the late King Abdullah and a former governor of Riyadh, and the interrogators may have been pressing the general for information about his boss, Prince Turki.

In November, al-Qahtani was taken to a hospital for radiological scans and other treatment, where he showed signs of having been beaten, according to a doctor briefed on his condition.

He was returned to the hotel for further interrogation, and later pronounced dead at a military hospital. The kingdom has never publicly provided an explanation of the general's death.

Whatever pressure was applied in the Ritz, the goal was to get detainees to sign over assets.

The kingdom's public prosecutor said in January that the government had reached settlements worth US$106 billion (S$140 billion), and other officials have said they expect the process to yield US$13 billion in cash by the end of 2018.

But separating those two figures is the fact that relatively little cash was seized, either because the detainees did not keep large sums in Saudi banks or because they hid their cash abroad, where the government could not take it without a substantive legal process.

There have been no clear indications that the government seized any foreign investments in the kingdom, nor succeeded in taking Saudi assets held abroad.

Most of the seized assets, according to financial advisers and associates of the detainees, were domestic real estate and shares of companies, which the government is expected to liquidate over time, a process that could take years.

One target is the wealth of the offspring of King Abdullah, the previous monarch. They were seen as potential rivals for the Saudi throne.

One of Abdullah's sons, Prince Turki, was removed from his post as governor of Riyadh in 2015, while another, Prince Mutaib, was dismissed as head of the National Guard in November. Both men, and a number of their brothers, were detained in the Ritz.

King Abdullah left tens of billions of dollars in the Abdullah Foundation, which was meant to finance projects in the king's name while also serving as a piggy bank for his heirs, according to three associates of his family. After he died in 2015, the foundation paid out billions of dollars to his more than 30 children, about US$340 million to each son and US$200 million to each daughter.

The crown prince is seeking to recover that money, which he believes was taken illegally from a charity, according to people familiar with the negotiations. King Abdullah's children, however, consider it their inheritance.

The foundation's administrator is Prince Turki, whose aide, al-Qahtani, died in custody. Prince Turki is still detained and most of his siblings and their families are banned from traveling outside the kingdom. Others are abroad in London and elsewhere, afraid to return to the kingdom that their father recently ruled.