Central authorities have begun briefing officials on findings of the corruption case centred on former security tsar Zhou Yongkang, signalling the final stage of one of the country's most significant graft investigations in decades. The briefings included new details about the possible origins of the case against the retired Politburo Standing Committee member, according to people who received the information. For instance, the decision to investigate Zhou last summer was made after findings of an inquiry into his former top aide Guo Yongxiang were presented to the top leadership. Guo - a former Sichuan deputy governor and Zhou secretary - was detained on suspicion of corruption in June. He was by then semi-retired in an honorary role as chairman of the Federation of Literary and Art Circles in Sichuan, a political power base of Zhou's. The briefings were seen as a sign the case against Zhou, who was until late 2012 one of the nine most powerful officials in the Communist Party, could be announced soon, perhaps after the Lunar New Year holiday. Such briefings for top-level officials are customary at the culmination of highly sensitive cases. Zhou would be first current or retired member of the Politburo Standing Committee to be charged with financial crimes. President Xi Jinping's decision to launch an unprecedented investigation against him was first reported by the South China Morning Post in August. Surprisingly, another key Zhou aide facing graft allegations, former Sichuan deputy party secretary Li Chuncheng , was not mentioned in the recent briefings. Li's detention weeks after Xi became party chief was one of the first public signs Zhou's circle had been targeted. "The information was delivered only verbally and it is very brief," one person with knowledge of the briefings said. Zhou was made the country's police chief in 2003 and oversaw the entire legal and law enforcement system from 2007. He retired from his top positions in November 2012, just after the corruption case against a key political ally, former Politburo member Bo Xilai , was formally announced. The corruption case against Zhou would overshadow that of Bo, who held a lower rank, and could prove the most spectacular since the "Gang of Four" show trial more than three decades ago after the Cultural Revolution. In recent months, party investigators have rounded up numerous former Zhou aides and close associates. Dozens of officials have been detained, including Jiang Jiemin , the former head of the state-owned assets watchdog, and Li Dongsheng , the former deputy national police chief. The nature of the potential allegations against Zhou is unclear, and has been the subject of much speculation. Media reports have alleged his involvement in everything from attempts to thwart Xi's rise to party chief to a conspiracy to murder his own wife. But the person familiar with the briefings said the investigation would deal exclusively with financial issues and corruption. It is also believed that the amount of money involved in the case would be far less than some reports have suggested. The difficulty in tying money directly to Zhou has been seen as one of the reasons the case has taken so long to build. Like Bo, Zhou is believed to have crafted an elaborate network to protect his family interests and cover the money trail. Most deals were said to have been done through third-party intermediates, the proxies holding most of the ill-gotten wealth.