A former secretary of ex-security tsar Zhou Yongkang is reportedly under investigation, joining three other occupants of the role who are already being probed for graft. Shen Dingcheng, the party chief and vice-president of PetroChina International, disappeared shortly before the Lunar New Year holiday, the China Business Journal reported, citing an anonymous source. Shen is among an extensive network of Zhou's allies who have been snatched by the authorities. They range from the Beijing city spy chief Liang Ke to Sichuan mining tycoon Liu Han , who is accused of running a massive mafia ring. The China Business Journal, which like other publications did not mention Zhou by name, said Shen became a secretary to "a particular leader at China National Petroleum Corporation [CNPC] at some point between 1992 and 1997". Zhou held the positions of deputy manager and general manager of CNPC at that time. The report also highlighted Shen's links with three other former secretaries to Zhou and even described Shen as being part of a "gang of four" secretaries. The other former secretaries are ex-CNPC deputy general manager Li Hualin, former deputy Hainan governor Ji Wenlin , and the former chairman of the Federation of Literary and Art Circles in Sichuan, Guo Yongxiang. All three are being investigated for graft. Shen's wife was also investigated, but was allowed to go home, the source added. Calls to PetroChina and its spokesmen went unanswered yesterday. Shen's profile as part of the management team of PetroChina International, a PetroChina subsidiary, remained on its website yesterday. Li was Shen's predecessor as deputy head of the party secretariat at CNPC's head office before 1992. Li was among three senior CNPC executives targeted by internal party investigators in August. Liang, whose dismissal was announced on Friday, was a key ally of disgraced deputy national police chief Li Dongsheng . Zhou's power bases were in the police, the oil sector and Sichuan, and it is an open secret that he has close links with fallen Chongqing party boss Bo Xilai . Communist Party leaders endorsed a decision to probe Zhou at their secretive annual meeting at Beidaihe in August last year, the Post reported earlier.