China is being purged. An aggressive anti-corruption campaign that began after Xi Jinping became chief of the Chinese Communist Party in 2012 and the nation's president the following year has shaken institutions from the army to the state television broadcaster. Hundreds of thousands of officials have already been detained. Unlike similar crackdowns of the past, the effort shows no signs of slowing.

"China's anti-graft campaign has moved beyond setting warning examples to deter others," said a 2014 year-end report from state press agency Xinhua. "The scale of the investigations, as well as new initiatives and legal reform, indicate that the country intends to fight a protracted war."

Xi's promise to eliminate both "tigers and flies" — the high-ranking officials who have stolen billions and the petty corruption that plagues everyday life — is genuinely popular among ordinary Chinese who saw graft worsen over the past decade. The president and his allies fear that corruption could lead to the overthrow of the Party itself if left unchecked. But while cleaning up, Xi also seems to be cleaning house, eliminating the power networks of former or potential rivals while preserving his own power bases.

Low-ranking officials are in a state of continual fear as their colleagues vanish around them. "There are so many rumors that I will be taken away, spread by my enemies," one county-level official told me.

The latest apparent casualty is Wang Tianpu, the president and vice-chair of the state-owned oil behemoth Sinopec, who authorities said on Monday had been detained while under investigation. Wang was once tipped as a rising star of Chinese politics, but his support had already been hollowed out at Sinopec. So many employees had disappeared by the end of last year that the personnel department began calling each morning to check that critical staff were still there.

China's legal system has recently been reformed to limit the power of police, restrict the use of torture, and keep the families of detainees informed. But the police have little to do with the anti-corruption crackdown. Instead, the sweep is being carried out by investigators with the Central Commission for Discipline Inspection, the Chinese Communist Party's top internal watchdog. The detainees vanish not into jails, but into the maw of shuanggui — a practice used by the CCDI to vanish and interrogate Party members who are under suspicion of "violations of discipline."

Interrogators who forced feces and urine into suspects' mouths referred to the mixture as 'Eight Treasures Porridge,' a popular Chinese breakfast.

On paper, shuanggui is a process of internal discipline and regulation within the Party; in practice it's a vast, brutal, extra-legal interrogative system into which people disappear, without recourse, for weeks or months at a time. The term, which means "double designation," refers to the government notice that informs Party members to appear for questioning at a "designated time and a designated place." But the earliest that officials are aware of their misfortune is typically when the CCDI interrogators arrive at their home or office to seize their mobile phones and disappear them into a shadow world.

Chinese legal scholars have privately compared shuanggui to the CIA's use of extraordinary rendition, in which a terror suspect is kidnapped and covertly interrogated outside of legal bounds. The CCDI's toolbox is similar. Officials under investigation are whisked away to isolated hotels, appropriated government buildings, or other secret locations.

Interrogators work in teams, rotating so that the same questions are asked again and again from different faces, keeping 24-hour schedules so that the suspects can be woken and questioned at anytime of day or night. Stress positioning and sleep deprivation are used to break suspects.

In some cases, so is physical torture. "It's very difficult to know the extent of physical or psychological torture," Flora Sapio, a China law scholar specializing in criminal justice and administrative detention, told me. As with all of the Party's inner workings, there is almost no external oversight of the detention process or the methods used. High-ranking officials are far less likely to be tortured, because of the embarrassment their death would cause and the risk that they might find a way to reverse their situation and take revenge.

Chinese President Xi Jinping (r) speaks with Wang Qishan, Secretary of the Central Commission for Discipline Inspection, who is tasked with implementing the anti-corruption campaign. (Photo via Reuters)

This disciplinary custom is technically illegal, or extra-legal. The Party regulates its application, but it has no existence or established role within China's legal system. While the government has been restraining or abolishing other forms of quasi-legal detention, such as the "rehabilitation through labor" system, the use and reach of shuanggui has only increased.

"Shuanggui is the first step of any interrogation because the political architecture of the Party system is Leninist, and Party discipline is a core concept in Leninism," Sapio told me. Under Leninist theory, the Party remains outside and above the state, an eternal guardian of the revolution. Though the government could legalize shuanggui at any time with minimum effort, it is kept above the law as a reminder of the Party's supremacy — an intimidating tactic that reinforces the practice's ominous reputation.

But few in China question shuanggui's legitimacy, and not just out of fear of causing trouble for themselves. Officials are widely seen as so powerful that ordinary methods are not enough to tackle them, especially after the rampant corruption of the 2000s. The internal process allows Party elites to regulate themselves. China's police are politically toothless, and highly reluctant to touch officials. The public has no trust in them, whereas CCDI investigators are increasingly painted as corruption-busting heroes.

What we know of shuanggui comes from accounts posted online or given to journalists by former provincial officials who have described it as a "a living hell," or from the rare cases of abuse that reach the courts. The Chinese press is rarely able to report on it, but survivors of detention have testified to a range of horrors. Beatings are a universal constant of such accounts, though more elaborate torture methods are also used, including waterboarding. Yu Qiyi, the chief engineer of a state-owned enterprise, drowned while in custody in 2013 after his head was repeatedly held under ice-cold water; his body was covered with numerous welts from other abuses. In one of the rare cases of interrogators being held liable by the courts, his six torturers were convicted.

Chinese justice has been obsessed with the primacy of confession since imperial times — an ideology only reinforced by Maoism and its 'self-criticism' sessions.

Zhou Wangyan, a Hunan official accused of bribery, told the AP that he was chained, had his left leg broken, and was forced to eat and drink excrement. Others report being whipped with wire, having their face pressed into coals, and being administered hallucinatory drugs to compel confession. Reflecting the cold humor commonly used by torturers to disassociate themselves from their prisoners, Zhou said that interrogators who forced feces and urine into suspects' mouths referred to the mixture as "Eight Treasures Porridge," a popular Chinese breakfast.

But the principal leverage comes from feelings of isolation, inevitability, and the knowledge that you have no way out and that your family is vulnerable. Under Partyregulations published in 2001, confinement under shuanggui can last up to six months. The process is often combined with house arrest for family members of officials under interrogation, which keeps relatives from calling in political connections on their behalf. Because shuanggui has no legal framework, there is no clear route to appeal for release, or even to know where someone is being held or for how long.

For these Chinese powerbrokers, isolation is a form of terror. The setup in some shuanggui facilities, rarely exposed to the public but described by a blogger in 2011, looks like a distorted version of the offices and conference rooms where officials usually spend their time. But here their every movement, down to going to the toilet, is monitored and accompanied. The dynamic of power they're used to is utterly reversed, and the outside world is shut off.

The power of confinement has grown under CCDI chief Wang Qishan, who appears to be Xi Jinping's closest political ally; the Bobby Kennedy to his Jack. Before 2012, CCDI inspectors faced severe constraints on their actions, as Australian journalist Richard McGregor documented in his 2011 book The Party. Party scholars told McGregor that top officials "flew above or beyond the system," and noted that CCDI personnel within ministries and state firms "either do not dare [to refer cases] or are not willing to." The use of shuanggui required higher-level officials within the CCDI to sign-off on the process, who were often pressured or enticed to scuttle investigations.

Officials feared investigation by the CCDI four years ago, but friends of mine who worked in government told me that they were more fearful of the Ministry of State Security, the Chinese equivalent of the KGB. "If you offend [the MSS], then they'll destroy you," a young official in the Ministry of Religious Affairs once told me, describing the fear that swept over her colleagues when MSS operatives came by. Her position was particularly ideologically sensitive, but the MSS was widely perceived as powerful, vindictive, and deeply corrupt. Yet today it's undoubtedly the CCDI that keeps officials awake at night.

The Mausoleum of Mao Zedong. (Photo via Flickr)

The MSS's power appears to have suffered with the drawn-out fall of Zhou Yongkang, China's former domestic security czar and oil chief, whom Xi and Wang waged a long campaign to bring down. After he had been missing for months, Reuters disclosed in March 2014 that the government had detained or questioned more than 300 of his relatives and associates and seized assets worth at least $14.5 billion. Zhou was officially arrested and expelled from the Party the following December, making him the highest-ranking government official charged with corruption since the Cultural Revolution.

The CCDI was strengthened in part to circumvent Zhou's control of the security apparatus, which he reportedly attempted to turn against Xi. Earlier this month, Bloomberg revealed that sources close to the investigation said that Zhou had spied on top officials (including Xi), collecting personal and financial information and leaking unspecified details to Chinese-language websites located overseas. Zhou's network in the oil sector also helps explain Xi's tiger hunt at Sinopec and the equally massive Petrochina, where numerous senior executives have also been detained.

Tracing the course of this power shift is difficult, and runs up against the near-total opaqueness of the Party's inner workings. Battles within the Party resemble the struggles of medieval barons more than they do anything we would recognize as party politics, complete with kidnappings, changes of alliance, dynastic regionalism, and factions that are generally more dependent on personal influence than ideological affinity. At the same time, they interweave with a powerful and heavily bureaucratic system.

Like many practices in the People's Republic, shuanggui draws equally from Chinese history and Soviet practice. Supra-legal inquisitions for officials were a common tool of emperors, but the practice of seizing officials and confining them to a "room of regret" was copied from the Soviets. Originally practiced by the Red Army as a form of military discipline, it became a tool of both punishment and intrigue, used by various Party groups against political rivals and corrupt officials. Over time it was standardized; by the late 1990s, it had become entirely the domain of the CCDI.

Chinese justice has been obsessed with the primacy of confession since imperial times — an ideology only reinforced by Maoism and its "self-criticism" sessions — and the aim of shuanggui is essentially to get the suspect to talk, not only about their own crimes but about those of their political allies.

Once investigators have what they want, suspects are turned over to rubber-stamp criminal courts, where they face almost certain conviction. In some cases, whether because of a lack of evidence or a political reversal, shuanggui suspects are spared indictment, but being detained still sullies their careers. The confessions made in detention are theoretically inadmissible, and the prosecution is supposed to re-gather the evidence — but this is widely ignored in practice. When disgraced Party chief (and close Zhou associate) Bo Xilai was tried for corruption, bribery, and abuse of power in 2013, his shuanggui confession was submitted in court because he would not repeat it.

Deaths while in detention, whether from torture or suicide, are considered failures, and in rare cases can result in prosecution. But detainee suicides appear to have diminished. Some 120 suspects were said to have killed themselves in the first two months of 2003 alone — a figure that might include the cover-up of deaths from torture — but a close watch on detainees today, and the restriction of interrogations to first-floor rooms to avoid sudden defenestration, seems to have reduced fatalities.

Xi's war against corruption remains massively popular, and there's little doubt that the "tigers" he has brought down were corrupt — perhaps even more so than the average. But his own family's wealth rivals that of any of the bloated plutocrats whose ruin he and Wang have engineered, and he appears to have used the corruption fight to weaken political opposition, so much so that it was only last month that the first senior officials from his regional bases were named in graft investigations.

Cleansing the Party is only partially the point. The increased use of covert discipline reinforces a message being instilled by other campaigns, such as China's wide-ranging crackdown on journalists, civil society, non-governmental organizations, foreign culture, feminists, and anyone else that might provide an alternative to Communist centralization: The Party is everything — and the only organization with the right to control it is itself.