Updated at 1:55 p.m. EST on 2014-07-29
The ruling Chinese Communist Party's anti-graft body on Tuesday announced a formal corruption probe targeting former security czar Zhou Yongkang, the highest-ranking official to be investigated publicly since its rule began more than six decades ago.
"As Zhou Yongkang is suspected of serious breaches of discipline, the Central Committee of the Chinese Communist Party has decided to ... launch an investigation," the party's Central Commission for Discipline Inspection (CCDI) said in a statement posted Tuesday on its official website.
Zhou will be investigated by the CCDI according to the party's constitution and laws related to party disciplinary procedures, the statement said.
"Serious breaches of discipline" is typically used by the CCDI to refer to corruption.
The announcement puts an end to months of speculation during which one key Zhou ally after another was probed by the authorities after President Xi Jinping announced a corruption probe targeting high-ranking "tigers" and low-ranking "flies" alike.
Political analysts say the move is unprecedented, because Zhou is a former member of the all-powerful Politburo Standing Committee, which has typically been regarded as off limits to the CCDI.
Liu Dawen, former editor of the Hong Kong-based political magazine Outpost, said the move had been long-expected, however.
"There were reports that Zhou Yongkang was under house arrest [as early as] July 18, when they detained his former secretary," Liu said.
"As for whether there will be any bigger tigers, I'd say not in the near future, because it is already enough of a headache how to deal with Zhou Yongkang, whether to try him in court or discipline him within the party," he said.
Former Xinhua news agency journalist Yang Jisheng, now deputy editor of the cutting-edge political magazine Yanhuang Chunqiu, agreed.
"Of course there are even bigger tigers than [Zhou], but whether they will go after them or not is another matter," Yang said.
"We'll have to see if they have that capability."
But Bao Tong, former top party aide to late ousted premier Zhao Ziyang, said a top-down anti-corruption campaign would never truly win public trust.
"If the anti-corruption campaign really depended on the efforts of the public, then we would know for sure it wasn't just another power struggle," Bao told RFA.
"But if it doesn't rely on the people's efforts, then power struggles are inevitable."
"I can say for sure that Zhou Yongkang isn't the last of the tigers, because an anti-corruption power struggle has its own momentum: once you start it, you have to keep going," Bao said.
"If you back off, you'll be left with nothing."
According to Willy Lam, a China politics expert at the Chinese University of Hong Kong, the announcement that Zhou will be investigated is a sign that Xi has succeeded in consolidating his power since taking the helm of the party in 2012.
"Xi Jinping's power is really entrenched now," Lam said on Tuesday in comments emailed to RFA. "He is riding high. He is the first person to break the unwritten rule that Politburo Standing Committee members are 'untouchable'."
"Xi will emerge as a strongman because he can use the anti-corruption card to punish or intimidate real and potential foes," he said.
Analysts said the probe into Zhou was nonetheless highly controversial among party elders.
"There are still a few people in the highest levels of leadership who are unwilling to break the taboo around prosecuting members of the Politburo Standing Committee," Hu Ping, New York-based editor of the Chinese-language monthly Beijing Spring, wrote in a commentary last week on RFA's Mandarin Service.
Hu said the announcement suggests that a public trial similar to that of Bo Xilai will eventually follow.
"They can't make the case against Zhou Yongkang public and yet not give him a public trial like Bo Xilai, because the damage to the legitimacy and authenticity of their anti-corruption campaign would be too great," he said.
Lam said the announcement was likely the result of some tough deal-making behind the scenes.
"There was a compromise struck," Lam said. "Various party elders including [former presidents] Jiang Zemin, Hu Jintao and [former premier] Li Peng, agreed to incriminating Zhou Yongkang on condition that Xi will not target other former members of the Politburo standing committee."
Zhou, 71, who was once a political mentor to jailed former Chongqing party chief Bo Xilai, stepped down from his post as Politburo standing committee member and head of the political and legal affairs commission in November 2012, where he wielded huge power.
His former post has since been downgraded to report to the all-powerful Politburo standing committee.
However, Xi would still be watching his back, Lam added. "If he were to make a mistake, his foes will unite and pounce on him," he said.
He said Zhou was likely to cooperate with the authorities because his son is already under close investigation for corruption.
"Zhou ... wants to save his son," Lam said, adding that he believes a suspended death sentence now looks a likely outcome for Zhou.
Sources following the investigation say dozens of Zhou's former colleagues, political allies, and family members have been detained or are helping the authorities with their inquiries.
Until now, China's tightly controlled state media has only obliquely mentioned the probe into Zhou's political and business empire, which spans the petrochemical and mining industries, a regional power base in Sichuan, and China's hugely powerful domestic security apparatus.
On Tuesday, a dedicated page on the popular Twitter-like service Sina Weibo drew more than nine million page views in just a few hours, as for the first time in months it became possible to keyword-search "Zhou Yongkang" on China's heavily censored Internet.
However, the comments page on individual posts failed to load in spite of a large number of reported comments.
Reported by Xin Lin for RFA's Mandarin Service and by Ho Shan, Wei Ling and Pan Jiaqing for the Cantonese Service. Translated and written in English by Luisetta Mudie.