Reports from China indicate that retired senior leader Zhou Yongkang is under investigation by the Central Commission for Discipline Inspection of the Chinese Communist Party (CCP), the equivalent of the “Internal Affairs” division of a police force.

The investigation into Zhou constitutes a major event in Chinese politics. No other Politburo Standing Committee member has been placed under investigation, at least not publicly, in recent memory.

Zhou rose to the CCP Central Committee in 1997 and was elevated to the CCP’s Politburo (the core of power in the Chinese system) in 2002. In 2007, he joined the inner sanctum of the Politburo Standing Committee, whose members constitute the true leadership of the People’s Republic of China.

Prior to his retirement, Zhou was the chief of the Chinese domestic security apparatus. As head of the Ministry of Public Security (MPS), he had responsibility over the Chinese police force, courts, and prosecutors and shared control over the People’s Armed Police, which is responsible for maintaining domestic order. Zhou’s background, however, was in the energy sector. Trained at the Beijing Institute of Petroleum, he rose to be vice minister of the Petroleum Industry and head of the China National Petroleum Corporation.

Since Xi Jinping has assumed the mantle of CCP General Secretary, some 182,000 Party members—including 32 at the vice ministerial level or above—have been investigated. Earlier this year, retired General Xu Caihou, former vice chairman of the Central Military Commission (the most senior uniformed position in the People’s Liberation Army) was taken from his hospital bed where he was being treated for cancer and placed under investigation. He was subsequently expelled from the Party.

Most notably, Bo Xilai, former party secretary for Chongqing (a provincial-level city) was arrested, charged with corruption, and expelled from the Party. In the process, his wife and brother were also placed under arrest. General Xu, Zhou Yongkang, and several other arrested senior officials all have past links with Bo.

Analysis of this turmoil in China abounds. To what extent is CCP General Secretary Xi Jinping consolidating his power? Is this a genuine attempt to tackle the massive problem of Chinese corruption? Or does this reflect other factors at work? What is certain is that the current crackdown constitutes a major political development, a reminder of how opaque politics is in China, even today, and something to pay very close attention to.