Gu Kailai, 53, who is married to Bo Xilai, the former party secretary of Chongqing and a member of the Communist party's Politburo, faces the death penalty after being formally accused, together with Zhang Xiaojun, a member of her household staff, of poisoning the 41-year-old.
In the first official comment on the case since April, the state Xinhua newswire announced yesterday that an investigation had found "iirrefutable and substantial" evidence of Gu's involvement in the businessman's murder.
It said she and her Harrow-educated son Bo Guagua, who has recently been studying at Harvard, had come into "conflict" with Mr. Heywood over their "economic interests."
However, in the latest twist to the biggest political scandal to hit China in decades, the statement added that as a result of the row, Gu had begun to fear for her son's safety.
"Investigation results show that Bo Gu Kailai, one of the defendants, and her son surnamed Bo had conflicts with the British citizen Neil Heywood over economic interests," the short dispatch said.
"Worrying about Neil Heywood's threat to her son's personal security, Bo Gu Kailai along with Zhang Xiaojun, the other defendant, poisoned Neil Heywood to death," it added.
"The facts of the two defendants' crime are clear, and the evidence is irrefutable and substantial," Xinhua said, adding that the case would be heard by the Hefei Intermediate People's Court in Anhui province "on a day to be decided."
Gu, a former lawyer, was detained in mid-April and has not been seen since. According to Chinese legal procedure, the trial should occur a maximum of six weeks after charges are laid.
It was not clear from the Xinhua statement, however, when exactly Gu and Zhang had been charged. One possible date for the trial is August 7, according to a "family lawyer" quoted by the Reuters news agency.
The timing of the trial could clear the air ahead of the once-in-a-decade transition to a new set of Chinese leaders this autumn. The case has split the top leadership of the Communist party, and has cast a shadow over the handover.
The charges against Gu come shortly after Patrick Devillers, a French architect and close associate, returned to China from Cambodia saying he would cooperate with the Chinese investigation.
Bo and Gu's son, 24-year-old Bo Guagua, an only child, is thought to have remained in the United States after graduating from his master's degree program in public policy at Harvard University's Kennedy School of Government earlier this year. He expressed a wish to one Harvard academic to study law.
Bo Xilai, once thought to be in the running for elevation to the all-powerful nine-man Politburo Standing Committee this autumn, is also in detention, in an unknown location, while being investigated for "a severe breach of Party discipline."
He could subsequently face criminal charges, although there was no mention of him in Thursday's report.
Mr Heywood was found dead in a room at the Lucky Holiday Hotel in Bo's city, Chongqing, last November. He is believed to have been poisoned with cyanide.
An old Harrovian, Heywood was an experienced China hand who had acted for years as an intermediary between Western and Chinese clients and who is believed to have been a member of Bo and Gu's inner circle.
The authorities in Chongqing originally attributed Heywood's death to excessive drinking, but a scandal unfolded after Wang Lijun, the city's police chief fled to the American consulate in Chengdu, a city not far from Chongqing, and divulged details of the crime.
The suggestion that Heywood had posed a threat to Bo Guagua's "personal security" is a significant shift in the narrative of the case.
Until Thursday, sources with knowledge of the investigation suggested that Gu had killed Heywood because he had threatened to reveal her attempts to move substantial sums of money offshore.
The change in narrative may be part of an effort to paint Gu, who has a known history of mental illness, as paranoid and unstable; possibly a mitigating factor in her defense. While she faces the death penalty if convicted of murder, it is widely thought to be an unlikely outcome.
It is not clear why the trial will be held in Anhui province. There is a suggestion that the investigation of the case was farmed out to a "neutral" province to depoliticize the process.
However, Anhui happens to be the home province of China's Supreme Court head, Wang Shengjun, a close ally of Hu Jintao, the Chinese president. Mr Wang was promoted to be the country's chief justice in 2008 despite having no legal qualifications or background.
Mr Wang is also thought to have fallen out with Zhou Yongkang, China's security tsar, and Bo Xilai's remaining ally on the Politburo Standing Committee. Holding a trial in Anhui may therefore ensure a smooth outcome for Hu and his allies.
Xinhua added that Gu and Zhang's defense lawyers had been given a chance to meet with the prosecution, usually an opportunity to review the evidence, and that Heywood's family had been informed.
Heywood's widow, Wang Lulu, has remained in Beijing since his death together with their two young children, despite holding a valid British visa.
A spokesman for the Foreign Office said: "We are glad to see that the Chinese authorities are continuing with the investigation into the death of Neil Heywood. We are dedicated to seeking justice for him and his family and we will be following developments closely."
