Bo was one of China's most powerful and charismatic politicians until he was ousted in the spring as the scandal surrounding Heywood's death unfolded. Observers say the party's main objective is to keep the focus tightly on the murder case and not on larger allegations of corruption that could further taint the regime.
International media were barred from the trial at the Intermediate People's Court in the eastern Chinese city of Hefei. Details of the case against Gu were provided afterward by Tang Yigan, the court's deputy director.
He said prosecutors told the court that Gu sent her aide, Zhang Xiaojun, to meet and accompany Heywood from Beijing to the southern megacity of Chongqing, where Bo was the Communist Party boss.
Gu and Heywood were business associates but had a dispute over economic interests, according to Tang, whose account matched details from the indictment reported in official media several weeks ago. Gu thought Heywood was a threat to her 24-year-old son, Bo Guagua, and decided to have him killed, said Tang, who did not specify what sort of threat Heywood posed to the son, a recent Harvard graduate.
On the night of Nov. 13, Gu went to Heywood's hotel and drank alcohol and tea with him.
"When Heywood was drunk and vomited and wanted to drink water, she then took pre-prepared poison that she had asked Zhang Xiaojun to carry, and poured it into Heywood's mouth, killing him," Tang said.
Heywood's friends and family have said he was never a heavy drinker, and they rejected investigators' initial conclusion that he drank himself to death. His body was cremated and no autopsy was performed.
Tang said the prosecutors believed the facts of the crime were clear and the evidence sufficient, and that "Gu Kailai is the main culprit and Zhang is the accomplice."
Before Thursday, the 53-year-old Gu had not been seen in months and has never publicly offered her side of the story.
Gu and Zhang are likely to be found guilty of intentional homicide, which carries punishment ranging from more than 10 years in jail to a life sentence or the death penalty. However, any mitigating circumstances, such as Gu's concern for her son's safety or that she suffered mental health issues or was acting to protect herself from danger, could lead to a more lenient sentence, said prominent Beijing-based rights lawyer Li Fangping.
The scandal came to light in February, when longtime Bo aide and former Chongqing police chief Wang Lijun suddenly fled to the U.S. Consulate in the city of Chengdu. Apparently fearing for his safety if he remained in Chongqing, Wang told American diplomats about his suspicions that Heywood had been murdered and that Bo's family was involved.
However, in a surprising twist, a man who attended the trial said the court heard evidence that Gu had reported her plans to Wang before she committed the crime, as well as after the deed was done. "Wang Lijun knew all about it, and even participated in planning it," said the man, speaking on condition of anonymity due to the secrecy surrounding the case and fear of government retaliation.
Gu's lawyer raised questions about how Heywood died, pointing to tests that showed the level of cyanide found in a blood sample from Heywood's body was not enough to cause death and that the blood sample appeared to have been tampered with, according to the man.
State broadcaster CCTV aired video during the day showing a calm-looking Gu being led into court with a sheaf of papers in one hand. She and Zhang both wore white shirts and neither was handcuffed. In a sign of the government's desire to keep the trial low-key, no report appeared on CCTV's main evening news broadcast, which is more widely seen and where sensitive content is more stringently controlled.
Chinese officials agreed to let two British diplomats attend, but the British Embassy in Beijing said it would offer no statement on the proceedings.
The quick trial contrasts with often-lengthy high-profile murder cases around the world. But it's common in China, where even the verdict can be delivered the same day in death penalty cases.
"It's very unusual for criminal trials (in China) to extend beyond a day," said Joshua Rosenzweig, a human rights researcher based in Hong Kong, who said trials are short in part because witness testimony is usually written, instead of delivered in person.
"It's very rare to see what you see in other countries, where a trial starts on one day and extends through many, many days," he said. "The process is very structured. A Chinese criminal trial is not a free-flowing process."
In Gu's trial, Tang said material evidence, written evidence, witness statements and other materials were presented.
He said Gu's government-appointed attorney told the court that Heywood bore some responsibility for the crime, although he did not say why. The lawyer also said Gu had "less than normal" control of her actions at the time of Heywood's death, and that she had informed on the crimes of others. Tang did not say what those crimes were or how she might have been impaired.
Zhang's lawyer asked for leniency, arguing he was only an accomplice, according to Tang, who said the court would study the evidence and the arguments and make a judgment at a date to be announced later.
On Friday, four former police officials from Chongqing will also go on trial at the same court, charged with covering up for Gu in Heywood's murder.
Security was tight around the courthouse, with police lines in front of each entrance and dozens of plainclothes security officers patrolling the streets of Hefei, a gritty industrial city in Anhui Province hundreds of miles from the scene of the crime. There is precedent in China for trying politicians far from their bases of influence, but distance may not have been the only factor in the choice of venue. Wang Shengjun, the head of China's Supreme People's Court, the country's highest court, was once in charge of the province's judicial system.
The scandal has drawn attention to political infighting that China prefers to keep secret and comes at a time when the government is preparing for a once-a-decade political transition at the 18th party congress later this year, where it will install a new generation of leaders.
Bo, 64, the son of a revolutionary veteran, was once a contender for one of those top jobs. But his overt maneuvering to reach the highest echelons of the Communist Party angered some leaders, as did his bombastic campaigns to bust organized crime and promote communist culture while trampling civil liberties and reviving memories of the chaotic Cultural Revolution.
In April, Bo was stripped of his most powerful posts and Gu was named a suspect in Heywood's murder. That was followed by her indictment late last month, which indicated that the leadership had closed ranks and reached a general agreement about the case and was ready to move forward with the trial.
Bo is in the hands of the party's internal discipline and inspection commission, which is expected to issue a statement about his infractions. That would open the way for a court trial with charges possibly including obstructing police work and abuse of power. Thus far, Bo has been accused only of grievous but unspecified rules violations.
Wang, the police chief, is being detained for unspecified reasons,