By Ben Blanchard
BEIJING (Reuters) - Chinese authorities have arrested former domestic security chief Zhou Yongkang and expelled him from the ruling Communist Party, accusing him of crimes ranging from accepting bribes to leaking state secrets and setting the stage for his trial.
Zhou, 71, is by far the highest-profile figure caught up in President Xi Jinping's crackdown on corruption.
He is also the most senior Chinese official to be ensnared in a graft scandal since the Communists swept to power in 1949 and the highest-ranking to be prosecuted since the fall of the Gang of Four in 1976 following the Cultural Revolution.
In a terse statement released by the official Xinhua news agency at midnight into Saturday, the party's elite decision-making politburo said Zhou's case had been handed over to judicial authorities.
The party began its probe into Zhou, one of China's most powerful politicians of the last decade, in July, following months of rumors and speculation that he was in trouble.
"The investigation found that Zhou seriously violated the party's political, organizational and confidentiality discipline," Xinhua said.
"He took advantage of his posts to seek profits for others and accepted huge bribes personally and through his family."
"He abused his power to help relatives, mistresses and friends make huge profits from operating businesses, resulting in serious losses of state-owned assets," the report said.
Zhou also leaked party and state secrets, took money and property either himself or through his relatives, Xinhua said, without providing details.
In a common accusation used to discredit fallen officials, Xinhua said Zhou had committed adultery with a number of women and had "traded his power for sex and money".
Party members are banned from keeping mistresses.
DEADLY TUMOR
Xi has warned, like others before him, that corruption is such a serious problem it threatens the party's very survival.
"(Corruption) is a tumor eating away at the party's health and its resolute excision is a necessary demand to uphold the party's character, aims and leadership and to consolidate the party's power and basis for exercising that power," the People's Daily wrote in a commentary on its website on Saturday.
Zhou was a member of the Politburo Standing Committee - China's apex of power - and held the post of security tsar until he retired in 2012.
He was last seen in public more than a year ago. It was not possible to reach him for comment and it was not clear whether he has a lawyer.
Several of his allies have been put under investigation in recent months, including Jiang Jiemin, former top regulator of state-owned enterprises, as well as Zhou's son Zhou Bin.
Zhou Yongkang joined the Politburo Standing Committee in 2007 while also heading the central Political and Legal Affairs Committee, a sprawling body that oversees law and order policy.
The security apparatus he ran expanded during his watch and consumed a budget that exceeded the official figure for military spending. He quickly earned the enmity of Chinese dissidents.
It is unclear whether Zhou will receive an open trial and the midnight release of the news underscores the limits of the party's transparency in such ultra-sensitive cases.
Legal experts say the party runs a risk of Zhou threatening to reveal state secrets if he gets an open trial.
HUNTING "TIGERS"
Sources with ties to China's leadership have previously told Reuters that Xi was determined to bring down Zhou for allegedly plotting appointments to retain influence ahead of the 18th Party Congress in November 2012, when Xi took over the party.
Zhou had nominated Bo Xilai, a charismatic politician with leadership ambitions, to succeed him as domestic security chief and had tried to orchestrate the younger man's promotion to the Standing Committee, the sources have said.
Bo later fell in a divisive scandal following accusations that his wife had murdered a British businessman in 2011. Bo's wife was convicted over the killing and Bo himself was jailed for corruption and abuse of power last year.
Xi has made fighting pervasive graft a central theme of his rule and has promised to go after "tigers" - senior officials - as well as those of lower rank who are implicated in corruption.
Xi has also pursued corruption in the military, announcing in June a probe into former senior officer Xu Caihou, who retired as vice chairman of the powerful Central Military Commission last year.
In ordering the investigation of Zhou, Xi has broken with an unwritten understanding that members of the Politburo Standing Committee would not come under such scrutiny after retirement.
Sources have told Reuters that Xi's predecessors Hu Jintao and Jiang Zemin had approved the formal investigation into Zhou.
Former top leaders in China usually wield a lot of influence behind the scenes in a political system that prizes consensus decision-making. Both Jiang and Hu, as former presidents and heads of the party, also still have allies installed in office.
(Editing by Mark Trevelyan and Gareth Jones)