Beijing (CNN) -- Chinese authorities have stripped former leader Bo Xilai of his legislative membership, and prosecutors announced they have him under criminal investigation, state-run news agency Xinhua reported Friday.
Once a rising political star, Bo's fall has thrown the ruling Communist Party into its biggest crisis in decades.
The People's Congress of Chongqing, a southwestern metropolis governed by Bo until early this year, has removed his national delegate status, Xinhua said.
The moves come ahead of China's 18th Party Congress, which is convening next month in Beijing. The body will decide who will occupy the top positions in the party hierarchy. Leadership changes once every decade.
The Communist Party expelled Bo last month. His leadership positions were taken away in April.
Bo was once a contender for the Politburo Standing Committee, the team of nine politicians who effectively rule China. But he recently has come under scrutiny, and news reports say he is accused of corruption, abuse of power and improper sexual relationships.
Investigators determined that his behavior tarnished the party's reputation, Xinhua reported, and discovered "clues to his suspected involvement in other crimes." The party investigators have sent their conclusions to judicial authorities.
The report said Bo made "severe mistakes" related to the killing of a British businessman -- a crime for which Bo's wife was imprisoned -- and a diplomatic incident involving his former police chief in Chongqing, Xinhua said.
It also cited influence peddling, bribery and womanizing as details found in the course of the party's investigation.
Bo is a charismatic and controversial politician. He launched a "smashing black, singing red" campaign in the southwestern city of Chongqing that promoted Communist ideology and zealously cracked down on organized crime.
His economic programs, which included millions spent on social welfare, made him a popular leader in Chongqing. But analysts say his populist policies and high-profile personal style were seen as a challenge to the more economically liberal and reform-oriented faction that dominates the current party leadership.
Bo's fortunes changed when the dramatic scandal involving him and his inner circle began to seep into the public realm. His wife, Gu Kailai, and family aide Zhang Xiaojun were arrested in early April, suspected of poisoning British businessman Neil Heywood.
Heywood died in November in Chongqing, where Bo was the Communist Party chief. His death was originally blamed on excessive alcohol consumption.
Bo was soon stripped of his top posts for "serious breach of discipline." In August, his wife received a suspended death sentence after a seven-hour trial. Days later, four senior Chongqing police officers were also sentenced to jail for covering up the murder.
In an e-mail dated early October obtained by CNN, Bo Guagua, the son of Bo Xilai and Gu Kailai who lives in the United States, reiterated his belief in his parents' innocence and asked his maternal grandmother to find a lawyer for his father.
"Although I miss my parents every minute, I feel they are with me in my heart," the younger Bo wrote. "Wherever they are, they will hold their heads high and be the fearless and transparent people that they are."
"I don't know politics -- but since the state wants to have the rule of law, I believe its decision on my father also must go through a fair legal process," he continued. "Now I am helpless and you are the person closest to me -- I would like to entrust you with the task of finding an appropriate lawyer to defend my father."
A friend of the Bo family, who declined to be named due to the sensitivity of the story, told CNN the family has hired two Beijing-based lawyers to represent the former politician in impending criminal proceedings. The lawyers have not been allowed to visit Bo but they don't expect a trial to take place for another few months, the friend added.
Wang Lijun, the former police chief of Chongqing, set off the Bo story on February 6, when he fled to the U.S. Consulate in Chengdu and told American diplomats that Gu was a suspected accomplice in a murder case.
After his request for asylum was turned down, Wang left the consulate and was taken away by Chinese officials. But his accusations rocked the world's most populous nation.
Wang was sentenced to 15 years in prison last month for defection, cover-up, bribe taking and abuse of power.
The party expelled Bo after an investigation of the killing and Wang's visit to the consulate, a trip made "without permission," Xinhua said.
The investigators said Bo "bore major responsibility" in the Wang incident and the killing, Xinhua reported.