China's Communist party has pledged a thorough and transparent investigation into the death of the British businessman Neil Heywood and the possible link to his wife and a purged senior cadre.
The public reassurance comes a day after David Cameron raised the issue in a Downing Street meeting with the Chinese propaganda chief, Li Changchun, and allegations of murder and cover-ups were debated in the House of Commons.
Heywood died last November in Chongqing, a sprawling municipality on the Yangtze river. Local authorities initially told his family and British consular officials that he died of alcohol poisoning and a heart attack.
But it has subsequently been alleged that he was killed by Gu Kailai, the wife of the former Chongqing Communist party secretary Bo Xilai, after trying to extort money from her.
The case has triggered the biggest – and the most public – political turmoil in China since the Tiananmen Square protests in 1989.
In an editorial, the state-run news agency Xinhua said the party would be diligent in its inquiry into Bo – who was sacked in March. "The CPC central committee has made a resolute decision to thoroughly investigate related events and release information in a timely manner," it said.
It is far from certain, however, that the case would have come to light had it not been for an attempted defection by Chongqing's chief of police. Wang Lijun, who had been investigating the case, sought asylum at a US consulate in March. US government sources said he feared for his life, according to the New York Times.
Wang was refused asylum but was kept from the local authorities, who surrounded the US consulate, until a senior official from Beijing came to pick him up, the newspaper reported.
It was only after this that the UK government lodged a request for the Chinese authorities to investigate Heywood's death – though suspicions had been voiced many weeks earlier.
Beijing has subsequently taken action. Evidence of a crime has yet to be made public in this heavily politicised case, which comes ahead of a once-in-a-generation shift of political power this October in which Bo had been expected to be promoted to a core position.
Concerns about the outcome were debated in the UK parliament on Monday. In a written response, the foreign secretary, William Hague, said: "We now wish to see the conclusion of a full investigation that observes due process, is free from political interference, exposes the truth behind this tragic case and ensures that justice is done."
The Xinhua editorial said the investigation was being carried out for the sake of the Communist party and the people. "China is in the middle of a social transitional process and it is a crucial test for the CPC to ensure the purity of the party's officials," it said.
Progress may be swift. Police are said to be investigating a Chongqing official who allegedly provided the poison used in the murder and then helped to arrange the cover-up.
Xia Zeliang, the Communist party secretary of Chongqing's Nan'an district, allegedly dispatched staff to guard the hotel where Heywood's body was found, according to the Financial Times.