Yesterday was International Tiger Day, and Chinese President Xi Jinping marked the occasion by hauling in the biggest kill of his 'Tigers and Flies' anti-graft campaign yet: Zhou Yongkang (pictured). Zhou is a retired member of China's most powerful committee and former head of the country's security apparatus. 

The innocuously worded announcement on Zhou's fate came from China's Central Commission for Discipline Inspection last night. He is 'under investigation' on 'suspicion of grave disciplinary violations,' which means he'll almost certainly be jailed for corruption.

Zhou is the highest-ranking member of the Communist Party to be brought down on corruption charges since 1949.

President Xi has said from the start that no Communist Party cadre is off limits when it comes to corruption investigations. This proves it. 

But Zhou's real crimes were likely his association with Bo Xilai and carving out an oil industry and security fiefdom that rivaled the power base built by President Xi on his way up. In this sense, Zhou's downfall is more reminiscent of a Mao-era purge. Many would say it is a purge, the target of which is all and sundry associated with former President Jiang Zemin. 

We'll know soon enough. If Xi's anti-graft drive is an honest attempt by a man who views himself as clean to root out the corruption that pervades the Party, we'd expect the intensity of the campaign to continue. If it wanes, then Zhou was likely the top target of a purge from the start. 

For now, Xi is all powerful. With Zhou, rival princeling Bo and powerful ex-General Xu Caihou (and the military) all brought to heel, the President would seem to have little to gain from expanding the tiger net.

Other big names have been suggested. Malcolm Moore at The Telegraph quotes sources that Wen Jiabao could be next. The former Prime Minister has been on the corruption radar since The New York Times reported in October 2012 that Wen's family had amassed billions during his time in office. The Telegraph also records a connection between Wen's son and Zhou Yongkang's son, Zhou Bin, who was reported as under arrest for dodgy business dealings minutes after news of his father's fate yesterday. 

Writing for the Jamestown Foundation earlier this month, Willy Lam suggests that Xi's 'purge' may now turn to the Communist Youth League and intimate associates of former President Hu Jintao. Lam points to the tightening noose around the neck of Ling Jihua, a close Hu ally. Ling's brother was arrested in June and his brother-in-law was detained in mid-July.

But the downfall of the Communist Youth League didn't start with Xi, and Ling also had a Zhou Yongkang connection. After Ling's son killed himself at the wheel of his Ferrari in March 2012, Jiang Jiemin, the former Chairman of the China National Petroleum Corporation and a Zhou protege, arranged a payment of millions of Yuan to silence the family of a female victim and a surviving passenger. The payment was made at the behest of Zhou, according to Reuters. Jiang was brought down in September last year and investigators have questioned him about the payment.

At present, the CCP's factional rivalries have been smashed. There would seem little incentive — and a lot of disincentives — to go after a names bigger than Zhou. Proceedings against Bo Xilai and ex-General Gu Junshan, whose patron was Xu Caihou, were initiated under the Hu-Wen team, which could suggest some degree of continuity between the administrations. Equally, however, those proceedings could have been an early indication of the power Xi was amassing behind the scenes as the transition took place. 

On an optimistic note, Zhou's fall may be good news for the Chinese economy. Xi likely needed Zhou in the dock to push through promised economic reforms. Powerful interest groups — such as the petroleum industry, atop which sat Zhou's confidants — had stymied reform under the weaker Hu-Wen administration. With Zhou out of the way, Xi may be free to enact the economic reforms pledged at last year's Third Plenum.