The official, Wang Lijun, sought asylum on 6 February, fearing for his life as Chinese security forces surrounded the building in Chengdu and asked the Americans to turn him over.
Mr Wang remains at the centre of the most seismic incident in China’s domestic politics since the Tiananmen Square massacre in 1989, after Mr Bo’s wife Gu Kailai was last week named as a suspect in the death last November of British businessman Neil Heywood and Mr Bo himself was suspended from the Politburo.
Mr Wang arrived at the US outpost with documents detailing accusations against Mr Bo and Ms Gu, but did not hand them over, American officials revealed yesterday.
The contents are not known, though one official said they consisted of technical descriptions of police investigations in the municipality of Chongqing, where Mr Bo, 62, was Party chief.
Mr Wang was allowed to make phone calls to officials in Beijing he hoped would help him. In the meantime, he startled diplomats with a revealing discourse on the murky intersection of power, politics and corruption in China.
“Not everything was coherent, as you would expect,” an official said, “but he did provide some good insights.”
The authorities from Beijing eventually arrived and took him into custody, and he is now under investigation for divulging internal Chinese affairs to the US. If charged with and convicted of treason, he could face a death sentence.
According to the officials’ version, US diplomats who oversaw his stay pre-empted any formal application for asylum because of the difficulties of getting him out of the country and questions about his eligibility.
“He was not tossed out,” a senior administration official said. Consular officials contacted Washington, with the diplomatic considerations reaching as far as the White House.
The incident occurred just one week before China’s likely future leader, Xi Jinping, was scheduled to visit Washington at the invitation of US vice-president Joseph Biden.
The US remains officially silent on the role its diplomats played in the downfall of Mr Bo.
“It would be incredibly foolish for the US to play any public cards in this very messy Chinese family feud,” said Orville Schell, director of the Centre on US-China Relations at the Asia Society. “If there is one thing the Chinese are neuralgic about, it is when their private affairs get aired before foreigners in an embarrassing way.”
It emerged on Tuesday that in a tense meeting on or about 18 January, Mr Wang confronted Mr Bo with evidence implicating his wife in the death of Mr Heywood, a former friend of the Bo family.
Mr Bo was so angry he ordered Mr Wang out of the office, but after composing himself he told Mr Wang to return and signalled that he would let the inquiry proceed.
Two or three days later, Mr Bo shunted Mr Wang aside in an apparent bid to quash the inquiry and protect his wife and his career. Mr Wang then fled to the US consulate in Chengdu.
Mr Heywood, 41, was seemingly poisoned last November after he threatened to expose a plan by Ms Gu to move money abroad.
Some observers have seen the rare vigour with which Beijing has treated the Bo case as being evidence that the affair is as much about internal party divisions as any desire to seek justice in the death of Mr Heywood.
The Communist Party said yesterday it is investigating the murder, following new appeals from the UK for a swift probe, free from poltical meddling.
The party’s central committee “has made a resolute decision to thoroughly investigate related events and release information in a timely manner, a manifestation of its high sense of responsibility to the causes of the party and the people,” the party statement said.
“Based on the facts made public so far, the Wang Lijun incident is a serious political event that has created an adverse influence both at home and abroad, the death of Neil Heywood is a serious criminal case involving the kin and aides of a party and state leader, and Bo has seriously violated party discipline,” the party statement said.