Sun was abruptly removed from office in July 2017 and put under investigation by the Central Commission for Discipline Inspection (CCDI).

[2] He was elevated to become secretary-general of the Beijing party organization from 2002 to 2006,[3] in December 2006, he was appointed as Minister of Agriculture as nominated by Premier Wen Jiabao.

In November 2012, after the 18th CCP National Congress, he was appointed a member of the Politburo and replaced Zhang Dejiang as party chief of Chongqing.

[5] It is not clear if Sun had any strong backing from former political heavyweights prior to his ascendancy to the Politburo; more likely, he was a consensus candidate whose loyalties crossed factional lines.

[10] Curiously, footage of Sun also appeared to be deliberately cut from Xinwen Lianbo coverage of the National Finance Work Conference - a meeting attended by all Politburo members.

Before Sun, the last incumbent Politburo member subject to investigation was Bo Xilai (also then serving as Chongqing party secretary) in April 2012.

[12] Prior to his downfall, political observers generally saw Sun as being groomed for a higher leadership position due to his relative youth and the diversity of his experiences; he had even been characterized as a potential successor to Xi Jinping.

Prior to the announcement of the investigation, Sun (along with Hu Chunhua) were seen by political observers as having almost certainly secured further advancement at the upcoming 19th Party Congress.

Tianjin (under Li Hongzhong) and Guizhou (under Sun Zhigang) also held expanded meetings of party cadres to declare their support for the decision.

[15] On September 29, 2017, the Central Commission for Discipline Inspection, with uncharacteristic zeal, announced the results of the disciplinary case initiated against Sun, merely two months after he was formally placed under investigation.

[16] Additionally, the commission said Sun became "highly bureaucratic, lazy and ineffective, led a degenerate and corrupt lifestyle, engaged in money-for-sex transactions."

"[17] During the investigation, Sun was said to have informed on a number of high-ranking officials in Chongqing, causing unprecedented fallout on the megacity's political scene shortly prior to the 19th Party Congress.

[23] Desmond Shum, ex-husband of Whitney Duan and business partner of Zhang Peili, wife of Premier Wen Jiabao, revealed more detail about Sun's background and the circumstances for which he could have been purged in his book Red Roulette: An Insiders Story of Wealth, Power, Corruption, and Vengeance in Today's China.

Evidently, Whitney and Zhang had "cultivated" his rise to power by positioning him as an ally to Hu and Wen, while ensuring promotions for him through backroom deals, as part of an ambitious plan of getting him to the Politburo Standing Committee, to become Whitney's main guanxi patron and ensuring future business deals and political influence for themselves after Wen Jiabao's retirement.

Desmond claimed that Whitney and Zhang facilitated his promotion to Party Secretary of Beijing, Minister of Agriculture, and later Party Secretary of Jilin and Chongqing (and his promotion to the Politburo) through Wen Jiabao and Zeng Qinghong, a Jiang Zemin ally whose family also had extensive business relationships with Sun as well (he himself was later investigated as part of Sun's arrest).

[24] Desmond claimed by 2012, the plan seemed to be on track and even better than expected as Sun and Hu Chunhua were regarded as the primary candidates for succeeding Xi Jinping in 2022.

Desmond noted two factors, first was that Xi selected Chen Min'er, one of his allies from Zhejiang Province to replace Sun.