China sentenced its former domestic security chief to life in prison on Thursday after a secretive trial. He is the highest-level official to fall in a sweeping anti-corruption campaign and the most senior figure to face judgment in more than three decades.

The downfall of the disgraced spymaster, Zhou Yongkang, has been presented in China as evidence that no official was safe from President Xi Jinping’s efforts to address chronic corruption in the one-party state.

But some experts said his downfall was also partly driven by a sense that Zhou had grown too influential and had shown disloyalty toward Xi.

Running the powerful state security apparatus, Zhou was feared and hated by many.

Zhou Yongkang, then a member of the Chinese Communist Party’s Politburo Standing Committee who was in charge of state security, attends a conference in May 2012. (Alexander F. Yuan/AP)

“It was basically the case of someone who had grown so comfortable with free-flowing wealth and illicit money for his own networks that he had forgotten how to be loyal to the source of this — the [Communist] Party,” said Kerry Brown, director of the China Studies Center at the University of Sydney. “The combination of venality and disloyalty did for him.”

The state-run Xinhua news agency said Zhou was sentenced after a closed-door trial in Tianjin, about 80 miles southeast of Beijing, that began May 22. It said the 72-year-old Zhou had pleaded guilty to charges of bribery, leaking state secrets and abuse of power and did not plan to appeal.

Cheng Li of the Brookings Institution said it appeared the authorities had cut a deal with Zhou to avoid a lengthy and potentially embarrassing trial.

It also marked another stage in Xi’s ruthless consolidation of power since he took over the leadership of the party in late 2012.

“The most important objective for Xi is to consolidate his power, to regain public confidence of the party, and to show that the anti-corruption campaign is real. This has been effective,” Li said. “Another factor is Zhou was notorious for corruption and abuse of power.”

Video of the trial judge reading the sentence was shown on state television, after which the judge asked Zhou if he understood and had anything further to say.

“I submit myself to the verdict of the court, and I do not appeal,” a white-haired Zhou said, bowing his head. “I recognize that I broke the law and that this caused great damage to the party’s cause. I again admit my guilt and am penitent.”

Zhou, like many Chinese officials, dyed his hair black while in office. But it has become increasingly commonplace to see toppled officials standing trial with their hair now gray, symbolizing their fall.

“The amount Zhou took in bribes is extremely large, but he confessed truthfully, regretted penitently and handed in all the bribes actively,” the trial judge said while reading the sentence, according to Xinhua.

The judge said most of the bribes — totaling 128 million yuan ($21 million), Xinhua reported — were taken by Zhou’s wife and son. The judge said that while the charge of leaking national secrets was also “extremely serious,” it had not had serious consequences.

Hence, he said, Zhou was given a “lenient” sentence. Corruption carries a maximum penalty of death in China, but that is rarely applied to party officials.

As a member of the Politburo Standing Committee, Zhou had access to the most closely guarded information on government and Communist Party affairs. The government had initially promised the trial would be open but conducted it entirely in secret. State media gave only broad outlines of the evidence against him.

Xinhua said the judges had decided to conduct the trial behind closed doors because it involved matters of national security. But experts said it was at least partly to save face for the party and to avoid too many awkward questions about how one of its senior-most figures could have been so corrupt for such a long time.

“Either the party knew and did nothing — simply accepting this sort of behavior — or it had no decent processes in place to deal with it,” said Brown.

“Zhou’s case has always been a bit of an assassin’s blade, pointing at past and current leaders and raising questions about their own actions. He either made them look powerless, complicit or stupid.”

Zhou was the highest-ranking politician to stand trial since the 1981 show trial of Mao Zedong’s widow, Jiang Qing, and other members of the “Gang of Four.” They were convicted of leading the purges, persecution and chaos of China’s 1966-1976 Cultural Revolution.

Zhou’s downfall breaks an unwritten rule, in place for decades, that shielded members of the Standing Committee from prosecution even after retirement.

Chinese media said the probe into Zhou covered his positions over decades, including his role as deputy general manager of the powerful China National Petroleum Corp., and as a Communist Party boss in the southwestern Sichuan province.

Zhou’s allies were believed to include officials who opposed Xi’s political ascent. Among them were Bo Xilai, the charismatic former party chief of Chongqing, who was sentenced to life imprisonment for corruption in September 2013, and Gen. Xu Caihou, who died in March of bladder cancer while under arrest on similar charges.

Murphy reported from Washington. Xu Jing in Beijing contributed to this report.

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