In early February, Bo Xilai, then Communist Party chief of Chongqing city, visited a military complex in Kunming, some 400 miles from his political base. It was home to the 14th Group Army, a direct descendant of guerrilla forces his father led in the 1930s.
A waxwork model of his father, Bo Yibo, is on display at the base. State media noted that Mr. Bo was there to "cherish the memory of revolutionary ancestors." But China's top political leaders saw it as something more alarming, according to Communist Party and military officials.
Mr. Bo was in severe political trouble. On Feb. 2 he had fired his police chief in Chongqing, Wang Lijun. On Feb. 6, Mr. Wang had fled to the U.S. consulate in Chengdu. Mr. Bo had breached his authority by dispatching his police far outside their jurisdiction in a failed effort to retrieve him. Mr. Wang wound up in Beijing, making allegations against the Bo family to state security officials, including that Mr. Bo's wife was involved in the murder of a British businessman.
By visiting the military base in Yunnan province, Mr. Bo appeared to be flaunting his revolutionary ancestry and courting political support from the People's Liberation Army at a time when his career was in crisis, according to Communist Party and military officials. "Bo's trip to Yunnan caught people at the highest level off guard," said one high-ranking military officer.
Mr. Bo's ties to the military and his irregular use of his police forces are now key elements of the investigation at the heart of China's worst political crisis in more than two decades, the officials said. The saga also could affect the contours of a planned leadership succession in the fall.
At least two prominent army generals have been questioned about their connections to Mr. Bo and other senior officers are under scrutiny, said officials, military officers and diplomats briefed on the situation.
Because of the turmoil, Hu Jintao, who is expected to step down as China's party chief this fall and president in March, is more likely to continue for another year or two as head of the Central Military Commission, which controls the armed forces, analysts said.
China said last month that Mr. Bo—once a front-runner for a position on the Politburo Standing Committee, the nation's top decision-making body—had been dismissed from his party posts and placed under investigation for unspecified "serious disciplinary violations." The government also said his wife was in custody as a suspect in the murder of Neil Heywood, a British businessman who was close to the Bo family.
One party official at an influential government think tank said that when he attended a party meeting at which Mr. Bo's dismissal as Chongqing Party chief was announced, his visit to the military base was listed as one of the main causes for concern. Ordinarily, visits to military sites by civilian leaders are strictly regulated.
Over the years, the relationship between the People's Liberation Army and the Communist Party has been politically sensitive. A founding principle of the PLA is that it answers to the party's central leadership. Over the past few decades, the party has tried to quash regional and factional loyalties that once pervaded the military. Mr. Bo's visit to Kunming touched a nerve because it suggested that, with his career in crisis, he enjoyed support in parts of the military because of his ancestry.
Mr. Bo's dismissal as Chongqing party chief in March briefly sparked rumors of a coup plot. Twitter-like microblogging sites circulated unsubstantiated reports of gunfire in central Beijing and large numbers of military vehicles and plainclothes police on the streets.
The officials, diplomats and military officers briefed on Mr. Bo's case said the coup rumors were off the mark. They said the two generals questioned about ties to Mr. Bo are Liu Yuan, political commissar of the PLA's General Logistics Department, and Zhang Haiyang, political commissar of the Second Artillery, which controls China's nuclear missiles. As commissars, they are responsible for personnel, discipline and political education. They have the same status as military commanders.
"Since Bo's dismissal, questions have been raised about their ties with Bo, and to whom they owe their loyalties," the senior military official said of the two generals.
The PLA and Defense Ministry declined to comment on the two generals.
Like Mr. Bo, both generals are part of an elite group known as "princelings" because their parents helped lead the party to victory in 1949. Gen. Liu is the son of a former president. The two have known Mr. Bo since childhood.
Other senior military officers have been asked to profess their loyalty to the current civilian leadership, especially those in the Chengdu Military Region, which includes Mr. Bo's former jurisdiction of Chongqing, according to diplomats, officials and military officers.
The controversy over Mr. Bo could influence a planned military leadership change this fall. In addition to installing new top political leaders, the party is due to replace seven generals on the 12-man Central Military Commission. Both generals questioned about Mr. Bo were in the running for promotion to that commission, both of them as potential heads of the PLA's General Political Department, which among other things handles discipline and political education in the armed forces.
There also are implications for Vice President Xi Jinping, a princeling who is expected to take over from Mr. Hu as Communist Party chief in the fall and as president at a parliament meeting in March. Mr. Xi is currently vice chairman of the military commission. If Mr. Hu stays on as its chairman, it will curb Mr. Xi's perceived authority and limit his ability to promote his favored generals.
The scandal could intensify debate within the military about whether it should continue to answer to the party, as it has done since its founding, or whether it should distance itself from politics by pledging allegiance to the state, as most modern armies do.
An editorial Tuesday in the Liberation Army Daily, a military mouthpiece, urged troops to be "unhesitant, unambiguous and unwavering" in the face of calls for the "nationalization" of the PLA. "Ensure that the gun always heeds the party's commands."
Control of the PLA—the world's largest standing army, with 2.3 million armed troops—has always underpinned the party's grip on power. Chairman Mao Zedong famously said that "political power comes from the barrel of a gun." Many of the party's early leaders, including Mr. Bo's father, were former military commanders.
After Mao's death, the army was sidelined from party leadership in an effort to prevent the kind of violent power struggles seen in the previous era. In exchange, the military was allowed to enter business. It swiftly built a commercial empire encompassing nightclubs, pharmaceuticals and hotels.
In 1998, then President Jiang Zemin ordered the PLA to give up its businesses in return for large annual increases in the military budget, which would enable it to become a modern fighting force.
But over the past decade, military analysts say, the PLA has again become involved in business, especially in developing land it controls. It also has become more active in policy-making, especially on issues such as relations with the U.S. and territorial disputes with China's neighbors. Military involvement in both areas—business and politics—has become a sensitive issue for the party.
The military looms large in Chongqing, home to a big PLA garrison and a PLA engineering university where weapons are designed. Mr. Bo, as Chongqing party chief and a Politburo member, was expected to have occasional contact with local and national military figures.
Mr. Heywood, the British businessman who was found dead in a Chongqing hotel room in November, told a friend that Mr. Bo regularly received generals at his residence and often criticized current political leaders as weak, according to that friend. Mr. Bo was "much more militaristic than people realized," the friend quoted Mr. Heywood as saying.
At issue now is whether Mr. Bo went too far by cultivating support among senior military figures—especially his fellow princelings—for his controversial policies and for his elevation to the Politburo Standing Committee, which he coveted.
Mr. Bo and his allies promoted a model for China's development based on stronger state intervention in the economy and society. It hinged on lavish spending on infrastructure, a high-profile crackdown on gangsters and a Maoist revival movement centered on mass renditions of "red" songs from the 1950s.
After launching those policies, he organized in 2009 a concert of revolutionary songs in Chongqing for some 200 sons and daughters of Red Army generals, including Gen. Zhang, according to state media reports at the time.
Mr. Bo lived in a military area, which he rarely left while in Chongqing, according to a city official who worked under him. In 2011, he poured about $500 million of public funds into developing a helicopter industry in Chongqing to meet the PLA's needs.
Last November, he hosted military exercises in Chongqing, attended by Defense Minister Gen. Liang Guanglie, after which Mr. Bo staged one of his "red singing" performances for his guests, according to state media reports.
Such activities left Mr. Bo's opponents increasingly wary of his widening military support, said officials, analysts and diplomats. The flight of Mr. Bo's police chief to the U.S. consulate—and Mr. Bo's defiant response—gave ammunition to his rivals to destroy his political career and discredit his model of government, these people said.
The scandal prompted President Hu to reassert his authority over the military. Four days after the investigation into Mr. Bo was announced on April 10, Gen. Guo Boxiong, a vice chairman of the Central Military Commission, visited the Chengdu Military Region and called for strict adherence to the party's central leadership.
He said officers and soldiers should be taught "not to listen to, believe, or spread any kind of political rumors, and to strictly guard against political liberalism," according to state media.
The scandal focused attention on the rapid rise within the military of the princelings, which has fueled discontent among officers who lack such political pedigree, and on the PLA's involvement in business.
Gen. Zhang, one of the generals questioned by authorities, is the 62-year-old son of a former vice chairman of the Central Military Commission. Before his appointment to the Second Artillery in late 2009, he was political commissar of the Chengdu Military Region, which brought him into Mr. Bo's political orbit.
He became one of several prominent generals to openly support Mr. Bo's controversial policies. Gen. Zhang also faces allegations from a former property tycoon that under his tenure, the Chengdu Military Region was involved in—and profited from—the seizure of assets from local businessmen targeted in Mr. Bo's crackdown on organized crime.
Li Jun, the real-estate developer, said in an interview that he bought a 110-acre plot of land in Chongqing's Shapingba district from the military. Mr. Li, a former soldier, said he was supposed to pay the military 324 million yuan ($51.2 million) by late January 2009, but that he missed the deadline and didn't pay until that June.
That December, he said, he was arrested by Chongqing police on charges of organized crime, contract fraud, bid rigging and bribery. About three weeks later, the Chengdu Military Region initiated its own case against Mr. Li and effectively took over his detention, according to a document provided by Mr. Li that appears to be signed by the military region's "political security department."
Mr. Li alleged his interrogators told him that he had upset Gen. Zhang, who they said had close ties since childhood to Mr. Bo. He claimed he was released after agreeing to pay 40 million yuan as compensation for his late payment. He fled the country, he said, after he was tipped off that he was about to be arrested again. Since then, he alleged, local authorities have taken over his company, Junfeng Group.
The Chengdu Military Region, the PLA, the Defense Ministry and the police all declined to comment on Mr. Li's account.
The website of his former company, Junfeng, says that its headquarters is at the same address listed for the Chongqing branch of the Chengdu Military Region's Materials Procurement Station. An official at that branch said it had sold "all of its land," but he declined to elaborate.
That address now is the site of a luxury villa complex developed by Junfeng, according to the company's website. A Junfeng sales representative said the company is no longer controlled by the Chengdu Military Region and is now under the authority of the local government. She declined to comment further.
"This kind of military involvement in a civilian case is highly unusual, even in China," said a person familiar with Mr. Li's case.
The other general questioned by authorities, Gen. Liu, is the son of former president Liu Shaoqi, who was purged by Chairman Mao and died in prison in 1969. Gen. Liu, who is 61, is thought to have personal ties to Vice President Xi, whom he has known since childhood.
Gen. Liu attended the elite Number 4 Boys Middle School in Beijing with Mr. Bo in the 1950s. In 2007, he was photographed alongside other princelings at the funeral of Mr. Bo's father.
Like Mr. Bo, he has spoken out against corruption. In January, he made a speech in front of several hundred other generals in which he pledged to root out corruption in the PLA, according to people briefed on the matter.
Early this year, he engineered the dismissal of Gen. Gu Junshan, the deputy head of the General Logistics Department, which handles military land and supplies, on suspicion of corruption, those people said. The PLA and Defense Ministry didn't respond to a request for comment.
Military experts said at the time that Gen. Liu appeared to be aiming for appointment as head of the PLA's General Political Department, which would give him a place on the Central Military Commission.
Some analysts believe he has antagonized fellow generals by rising through the ranks faster than non-princelings, by targeting Gen. Gu without the consent of his peers and by seeking to influence domestic politics.
"He was already politically vulnerable," said Nan Li, an expert on the Chinese military at the U.S. Naval War College. "The Bo Xilai incident might be the last straw on the camel's back."
Gen. Liu also generated controversy when, in the preface to a book published last year, he argued passionately in favor of "new democracy"—a concept put forward by his own father.
Zhang Musheng, a prominent public intellectual who wrote the book, also has spoken out in defense of Mr. Bo's "Chongqing model." He has been conspicuously silent since Mr. Bo's downfall.
Mr. Zhang said in an interview he had been due to speak about "new democracy" at a conference in the U.S. last month, but he canceled after a retired senior official advised him that the timing was too sensitive. He declined to comment on Mr. Bo's dismissal or its effect on Gen. Liu.
"You'd better not make a fuss about this," he said before hanging up the telephone.