Graft-busters on the mainland are closing the net around a powerful family headed by Ling Jihua, for long the right-hand man of former president Hu Jintao. Ling Wancheng , the youngest of the five Ling siblings, recently left China for the United States via Hong Kong and Singapore but has since returned to the mainland, where he is under investigation, sources say. It is not clear if the businessman, better known as Wang Cheng, returned of his own volition or as a result of cooperation between China and the US. Hu has been conspicuously silent over the investigation. In August, anti-corruption investigators detained Ling Zhengce , the elder brother and a senior official in Shanxi province. The detention of Ling Wancheng will help authorities prepare a move against Ling Jihua, the second-youngest and most powerful of the five siblings. Sources said the investigation against Ling Jihua could start soon after the Communist Party leadership wraps up its agenda-setting meeting today. Ling Jihua was on the fast track to the highest reaches of political power before his career was ruined in 2012 by the scandalous death of his son in a Ferrari crash. But even after his fall from grace, Hu's trusted top aide has held on to a ministerial position as head of the party's United Front Work Department, a vice-chairmanship of the Chinese People's Political Consultative Conference and membership of the party's elite Central Committee. For the better part of Hu's presidency, Ling Jihua, although not a Politburo member, commanded power and influence far greater than his position and party ranking suggested, becoming known as a go-to man in mainland politics. If the case against Ling Jihua goes ahead, it will be the biggest political scandal since the fall of former security tsar Zhou Yongkang . Ling Jihua would also be the second major political figure to be brought down by President Xi Jinping's anti-graft campaign . Sources said Xi was determined to make the campaign a permanent feature of the party's fabric. Xi and ally Wang Qishan - who is overseeing the crackdown - were in "no rush" to complete the investigation against Ling Jihua, a source said. They would allow time for investigators to gather evidence and build a solid case before making a move. Sources said the investigators had compiled a list of people close to Ling Jihua and his family, and sent the names to all mainland banks with discreet requests for financial information. The investigators were using supercomputers to sift through the mountains of data to follow any money trails. Unlike his two brothers, Ling Wancheng stayed out of politics, becoming a successful businessman and enthusiastic amateur golfer, sources said. "Wang Cheng" was a familiar name at Beijing's top golf clubs and he had several amateur championships under his belt. In 2009, he was elected a member of the China Golf Association. Sources described him as a low-profile person who only played the game with a trusted chosen few. While rumours about the corruption investigation against Ling Jihua have circulated for months, some saw his appointment as a CPPCC vice-chairman as a sign that he had escaped the crackdown. But as a sweeping anti-corruption campaign hit the Ling family's power base in Shanxi this year, the family again became the topic of speculation in the corridors of power. Born in Pinglu county in Yuncheng in Shanxi, the Lings were instrumental in the rise of the Yuncheng clique of cadres from the city, which came to dominate the province's politics. The crackdown in Shanxi led not only to Ling Zhengce's downfall - a brother-in-law, Yuncheng deputy mayor Wang Jiankang, was held for months before being released and allowed back to work. Wang is married to Ling Jihua's elder sister, Ling Luxian . Ling Jihua is also tied to Chen Chuanping , the sacked party chief of Taiyuan . According to sources close to Chen, the crashed Ferrari was a gift from Chen to Ling through the Taiyuan Iron and Steel Group, where Chen was once chairman.