China's leaders want Bo Xilai's downfall seen as a blow against corruption _ not as part of a power struggle. But with a second, even higher-ranking Politburo member now suspected to be under pressure, it will become difficult to avoid the perception of all-out infighting.

Moves against Zhou Yongkang, China's security chief, could undermine attempts to portray the Bo scandal as a fight to uphold the rule of law and would reinforce a skeptical public's view that the Communist Party is in disarray months before a once-a-decade transfer of power to new leaders.

In keeping with China's closed political system, the information released publicly about Bo's case has been little, the rumors many and almost no one is willing to speak on the record.

But overseas-based Chinese websites and political insiders are now saying that Zhou, one of nine members of the party's all-powerful Politburo Standing Committee, is also under heavy scrutiny and could face a reckoning.

"Internally, the power struggle is getting more intense and, if true, Zhou's removal would be seriously damaging," Beijing-based political analyst Li Fan said.

Zhou, 72, is widely reported to have been the only leading official to have argued against last week's striking decision to suspend Bo's membership in the 25-seat Politburo _ a step that effectively ended the political career of one of China's most ambitious and high-profile politicians.

Bo, 62, also has been removed from his position as party chief in the city of Chongqing and is now under investigation for disciplinary violations, possibly relating to corruption or interference in police work. His wife, Gu Kailai, and a household aide were named as suspects in the murder of British businessman Neil Heywood and handed over to police.

Since then, Zhou has made tearful self-criticisms to President Hu Jintao and former leader Jiang Zemin, his political mentor, according to the U.S.-based Chinese-language dissident news site Boxun.com, which has been reporting accurately on the Bo scandal. Despite that, Zhou is now under some form of secretive investigation by the party's disciplinary body, it said.

In a telephone interview, Boxun's manager, Watson Meng, said his sources say the investigation's outcome will be decided based on Zhou's attitude and will become known within days. A prominent Beijing lawyer, who asked not to be identified because of the sensitivity of the matter, told The Associated Press he heard the same from his sources.

Zhou's alleged crimes aren't known, although speculation ranges from massive corruption to secretly conspiring with Bo to boost him into the top leadership rungs.

Zhou for now remains very much in the public eye. On Tuesday, he greeted Cuban guests at a meeting carried on national television and also reported on the front page of the party's official People's Daily.

Bo and Zhou's relationship is believed to date at least as far back as the 1990s, when both served in the northeastern province of Liaoning. Close ties were underscored by Zhou's vocal support for Bo's signature policies as party boss of the southwestern metropolis of Chongqing of cracking down on organized crime and promoting Maoist culture.

On a well-publicized March 2010 visit to Chongqing, Zhou applauded the controversial decision to imprison lawyer Li Zhuang on charges he prompted a gang boss he was representing to lie about police torture. Li served 18 months in a Chongqing prison.

Zhou offered further praise at a meeting of Chongqing delegates to the annual legislative session last month, at a time when Bo was already under a cloud. Bo responded by pledging to "seriously reflect on and implement" Zhou's "important guidance."

One week later Bo was gone, sacked as Chongqing's leader after being publicly rebuked by Premier Wen Jiabao at a nationally televised news conference.

Bo rubbed many in the leadership wrong with his flair for self-promotion and willingness to deviate from party consensus. Zhou has been less controversial, although his support for Bo even when he was out of favor could be seen as a violation of party discipline.

Bo's removal has fueled cynicism among ordinary Chinese, leading to a flood of rumors and speculation _ much of it online _ about political feuding among the leaders and even attempted coups. Taking down Zhou would only reinforce such views, said Joseph Cheng, who heads the Contemporary China Research Center at the City University of Hong Kong.

"It furthers the perception that all cadres are corrupt and all corruption investigations are political," said Cheng, who believes Hu would prefer to sidestep further conflict by allowing Zhou to retire after this fall's party congress as originally expected.

While the speculation about Zhou simmers, other reports point to numerous detentions of Bo associates, either over corruption or in connection with the death of Heywood, whose once warm personal and business relationship with Gu and her son Bo Guagua had recently turned sour.

Targets in the probe reportedly include Xu Ming, multimillionaire chairman of the Dalian Shide Group and a Bo confidante, and Xia Zeliang, head of Chongqing's Nan'an district, where Heywood was found dead. Both men have dropped from sight since Bo came under investigation.

Meanwhile, the fate of the man who triggered the scandal remains a mystery.

The scandal was set in motion when Chongqing ex-police chief Wang Lijun visited a U.S. Consulate in the city of Chengdu, leading the British government to later request a new investigation into Heywood's death, which had originally been attributed to excess drinking or a heart attack.

Wang was Bo's former right-hand man in a campaign to crush Chongqing crime gangs, but he is believed to have enraged Bo by telling him of his suspicions about Gu's involvement in the Heywood case.

After leaving the consulate Feb. 7, Wang was taken to Beijing by investigators and there have been no official statements on him since. The U.S. has repeatedly refused to discuss anything that was said or done during his overnight stay.

The whereabouts of Bo's son, Guagua, a 24-year-old Harvard graduate student, also are unknown.

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Associated Press writer Isolda Morillo contributed to this report.