"I concluded he was very kind and considerate after long-term observation," Gu said. "He does not have the air of a businessman. Of course he was not a very big businessman at the beginning. So we didn't take him as an outsider." She used his contacts - and money - to buy things such as airline tickets.

A family employee, Zhang Xiaojun , testified that Xu was one of the few people able to contact the couple directly.

"He could dine at Bo's home. Sometimes Bo would take a walk with him. Xu was very close to Bo and Gu," he wrote.

In 2001, Xu paid €2.3 million on Gu's behalf for the purchase of a villa in France, setting up several companies and taking a loan from a bank in order to evade taxes and keep Bo and Gu's link to the property secret.

French architect Patrick Devillers found the villa and purchased it in the name of several newly registered companies on Gu's behalf. He leased it out until 2007, when Devillers was told by Gu that "his name was too sensitive in China, too", according to written testimony by Devillers.

British businessman Neil Heywood took over the villa, but his relationship with Gu went sour in a row over commission on a business project, Devillers said.

Devillers said he received a call in May 2011 from Heywood. The Briton sounded furious with Gu, saying that he had been cheated. Heywood allegedly threatened to "expose all" if his demand for £1.4 million (HK$16.9 million) was not met, Devillers said.

Gu said her relationship with Heywood deteriorated as she believed he posed a threat to the safety of her son Bo Guagua , who was studying at Harvard.

"Guagua gave me a video call with his iPad one day during the second half of the year [2011] and said Heywood threatened him," Gu said. "The image quality was bad and got cut off after several words. I was very worried about his safety. [Former Chongqing police chief] Wang Lijun was present as well. We all feared that Guagua might be killed in the US."

Xu gave the court more details of how Wang, whose attempt to defect to the US blew the lid off the Chongqing scandal, first grew close to the man whose political career he would later destroy.

Wang was police chief in Tieling when he was introduced to Gu by Xu, when Bo was Liaoning governor. Gu was dissatisfied with the handling of a case involving a member of the family's staff and asked Xu to recommend someone who could help.

Wang's testimony revealed just how close he became to the family. He said Gu was "very angry" at Bo Guagua for getting a girlfriend, and demanded that he return home from the US so she could scold him. It was Wang who made the telephone call to Bo Guagua.

Gu even confessed to Wang that "Heywood collected rent of seven to eight million yuan [on the villa] but gave me none."

Bo Xilai also confided in Wang and asked him to give Gu some advice after she had a fight with Heywood in July 2011.

Gu said she saw the threatening e-mail exchange between Heywood and her son and became more worried. Wang arranged for people to protect Guagua, but she "got more anxious, which led to the murder [of Heywood] on November 15".

The villa returned to Xu Ming's ownership in 2011 and later passed to his girlfriend, former television celebrity Jiang Feng Dolby. Jiang became a British citizen by marriage in 2004 and has two children.

According to Bo's defence lawyers, Jiang testified that the aim of her relationship with Xu Ming was "getting married" and that her understanding was that she would take over the villa because "Xu Ming wanted to get back his overseas assets and the villa would be a family villa for us". She later told prosecutors she knew she was holding the villa for Gu.

Bo's defence cast doubt on that explanation.