With Chinese politics roiled by the purge of Bo Xilai, a former provincial Communist Party chief, there are growing questions about whether the corruption and murder scandal that felled him might reach into the Party’s highest echelon to undercut an official considered Bo’s staunchest ally and defender.

Zhou Yongkang, China’s top official in charge of the country’s internal security apparatus, is considered close to Bo, and was the most prominent backer of some of Bo’s most controversial measures in Chongqing. Those included Bo’s ferocious clampdown on organized crime, his social welfare policies and a campaign to revive “red” culture that many saw as a worrying throwback to China’s violent Cultural Revolution.

Bo was dramatically removed from his post in Chongqing last month, and on April 10 stripped of his membership in the Party Central Committee and the 25-member Politburo. Authorities said Bo is being investigated for “severe violations” of the Party’s internal discipline rules while his wife and a household aide were arrested on suspicion of killing British businessman Neil Heywood.

As the scandal continues to unfold — fueled by Internet rumor and reports on overseas Mandarin-language Web sites hostile to the Chinese government — speculation has now centered on Zhou’s relationship with Bo, and whether Zhou might eventually become the next casualty of the Communist Party’s biggest leadership crisis in more than two decades.

Zhou’s future and fate are of more than passing interest here, since he is one of the most powerful, if less visible, figures in the Chinese Communist Party, with control of the vast security forces and the judiciary, including all the prosecutors. He sits on the nine-member Politburo Standing Committee, which effectively runs the country as a kind of collective leadership; its other members include China’s president and prime minister.

Zhou Yongkang, seen attending the National People's Congress in March, is reported to have been the only leading official to have argued against last week's striking decision to suspend Bo Xilai's membership in the 25-seat Politburo. (Andy Wong/AP)

The speculation intensified this week with the release of an April 17 Xinhua editorial hinting that more high-level firings may be coming. “The investigation into Bo,” the editorial said, “serves as a declaration to all Party members that no matter what position one holds, Party members shall never place themselves over Party discipline and the law.”

Chinese authorities have released little about their ongoing investigation into Bo, his wife, Gu Kailai, or other associates in his Chongqing inner circle who have been detained. In the vacuum of real information, citizens who have been closely following the saga through overseas Internet reports, and outside China-watchers, have been trying to glean information from the most innocuous signs, such as how much or how little a senior leader appears in the official media.

Zhou’s past and present statements and appearances are being closely dissected for any hints of internal strife.

For example, on March 8, during the annual meeting of China’s national legislature, Zhou made a highly-public appearance before the delegation from Chongqing, heaping praise on Bo and his achievements. Bo at the time was already reeling from his former police chief Wang Lijun’s flight to the American consulate in Chengdu, where Wang first outlined a dramatic tale of political intrigue, corruption and murder in Chongqing.

But exactly a week after Zhou’s high-profile endorsement, Bo was removed as Chongqing Party chief. Zhou then disappeared for a week from state-run television and newspapers, leading to questions about whether he had been sacked — and the period coincided with persistent, unsubstantiated rumors of a rift in the top ranks, or the wild rumor that Zhou was leading a coup. Then a March 23 photograph showed Zhou meeting the visiting Indonesian foreign minister, seeming to temporarily dispel the rumors.

Zhou’s most recent public appearance — on April 12, with the Shanghai Cooperation Council, and an April meeting with a visiting Communist official from Cuba — also seemed to quiet the continuing Internet-based chatter that he was being investigated, or on his way out. Still, the speculation has not died down entirely; as some have noted, Bo himself also appeared in public until the day before he was sacked as Chongqing chief.

Deep connections

In the past, when China’s Communist Party was led by strongmen such as Mao Zedong and later Deng Xiaoping, a top official could be removed instantly — as when Deng removed Zhao Ziyang as Party general secretary in 1989 because of Zhao’s sympathy for pro-democracy protesters occupying Tiananmen Square.

But some experts who analyze China’s secretive elite politics say the more diffuse nature of the current power structure could protect Zhou from trouble. While removing a member of China’s broader Politburo is not unheard of, they say, it would be far more problematic to remove one of the nine Standing Committee members.

Zhou is 71, and had been expected to step down this fall at the time of the 18th Party Congress this fall, a gathering that will usher in a new generation of leaders, led by Vice President Xi Jinping, who is all but assured to become president. Forcing out a septuagenarian months ahead of his retirement might be too tumultuous, some said; rather, he might be allowed to retire, and, like other fallen officials, remain in obscurity.

“I don't believe that Zhou Yongkang is really in danger now,” said Li Datong, an independent social analyst. “The Party will totally lose credibility in the eyes of the Chinese if even a Standing Committee member has violated the law and the Party’s discipline rules.”

Zhou and Bo’s connections go far back, despite their widely divergent backgrounds and the 10-year age difference.

Zhou, an engineer and graduate of the Beijing Petroleum Institute, was the general manager of the state-run China National Petroleum Corporation before he became a minister and Party chief in Sichuan province under former president Jiang Zemin. Bo, the “princeling” son of a revolutionary hero, Bo Yibo, is also considered a protégé of Jiang’s.

During that March meeting of the legislature, when Zhou dropped by the Chongqing delegation, Bo also showered Zhou with compliments. Bo noted that when Zhou was the Sichuan Party chief, he promoted the development of both Sichuan and Chongqing. Bo also noted how Zhou had visited Chongqing at the height of Bo’s crackdown on crime, inspecting the local police and public security forces and giving prominent backing to Bo’s anti-crime efforts.

Zhou was also the most prominent booster of Bo’s “red revival” campaign that included gathering students, government bureaucrats and others together in public parks to sing revolutionary anthems. Zhou attended a red singing performance in November 2010, and said he might launch the same movement in the judiciary system.

Still, it remained uncertain whether Zhou would be swept up in Bo’s scandal. Cheng Li, an expert on China’s leadership with the Brookings Institution, said some rumors about Zhou — including the notion that he he was plotting a coup — have already been proved false, but others may have merit.

“My sense is that at least for now, the top leadership does not intend to go beyond the Politburo level for various reasons,” he said. “Stability and unity are among the most important. But no one knows how the whole story will unfold in the weeks and months to come.”

Washington Post researcher Zhang Jie in Beijing contributed to this report.