Du had been a partner in a herbal remedies store with Helen Chui, the schoolteacher wife of university lecturer Jifeng 'Jeff' Ding. Last Sunday, the couple were found stabbed to death along with daughters Nancy, 18, and Alice, 11.

Behind the horror is a story of bad blood and legal wrangles over a number of years that was played out again in court just hours before the horrific rampage.

Now police hunting the prime suspect believe the suicide note was a lie and Du, who had a considerable amount of cash with him, is in hiding. Officers have not ruled out the possibility that he may have left Britain and fled to his native Hunan province.

Last night Detective Superintendent Glynn Timmins, the man leading the investigation, said it was possible Du had slipped out of the country.

'If he is hiding here or whether he's fled the country, the one thing is that he is alone and frightened and in that situation we would expect someone to find themselves somewhere they know or where there are people around who speak the same language,' he said.

'If he tried to lie low anywhere else then he may stand out. He had a significant amount of money with him, enough to sustain him for some time and certainly enough to get him out of the country.'

At the centre of the business dispute was Du's growing resentment against Helen Chui and her husband, who he believed had cheated him out of money and were trying to slither out of paying him by selling their home cheaply.

The long-running row, which dates back to 2004, involved a string of increasingly bitter legal cases, including one that was played out at the highest court in Britain.

Du had opened a herbal medicine shop with Chui in Northampton and they also owned at least two other shops, including one in Birmingham. However, the partnership did not go well and the former associates bitterly fought each other through the courts over debts that amounted to 'tens of thousands of pounds'.

It emerged that Chui and Ding were ordered to pay Du and his wife GBP30,000 (HK$384,000) after losing a court case in November 2007. Six months later a court in Bristol ordered them to pay 'a further interim payment of GBP30,000'.

Their former associate then won another court order securing the debt against the Ding's house, but the following day the couple attempted to sell their home to a Northamptonshire-based businessman and friend, Paul Delaney, for GBP210,000.

Du and his wife attempted to prevent the sale, claiming the Dings were deliberately undervaluing their home to put the family's assets beyond their reach. They claimed the house was actually worth GBP275,000.

They then launched a civil suit against Delaney to stop the sale and initially won a district court ruling, blocking the sale, but that was finally defeated in the High Court, in a landmark case, last year. Hours before the killings Du was handed an injunction that froze his assets; police say that was the 'final straw'.

Timmins, who said he was still trying to establish how the parties became business partners, said: 'Speaking to people, it seems apparent that Helen Chui had ideas that went beyond owning some shops. She wanted a bigger, better business.

'Du and his wife had the feeling that the Dings were taking more than the 50:50 share of the profits they had agreed, so they tried to sue the Dings to get the money they felt was rightly theirs and initially he was successful, but the Dings appealed and it was upheld.

'Then he began to suspect that they were trying to dispose of their house as an asset of the business. They went from legal wrangle to legal wrangle, right up until the day before the murder.

'This row would have probably gone on for years, but for these terrible events. I have considered the idea that this may have been about Mr Du's loss of face, but it seems to me that this is simply about a growing level of animosity between two families.'

The latest ruling seemed to have pushed Du over the edge, Timmins said. 'What I can't say is what was in his mind when he made that visit. I'm sure he intended to confront the family. I'm sure he was angry about the court action that had been taken between the two families, but did he intend what happened?'

Last Friday, Du set off for work leaving his silver BMW parked outside his semi-detached home in Coventry. He was last seen that lunchtime when he shut his shop in Pallasades Mall in Birmingham's city centre. He left a note written in Chinese behind.

Cryptically, the short message, which was addressed to the members of his family and contained little detail, said: 'There is always a time to say goodbye.' He asked that his loved ones take care of each other.

'I am not convinced this was a suicide note,' Timmins said. 'In my opinion, this was a note written by someone saying goodbye, who was not intending to come back.'

What is also unclear is Du's background before his arrival in Britain in the late 1990s. He was granted indefinite leave to stay in the country four years later and became a citizen in 2004.

'We are not sure about Mr Du's background in China, but we know he came from the Hunan area and arrived here in the UK in the late 1990s,' Timmins said. 'We believe that his wife came with him.

'Checks are still being made with passport agencies and the Chinese embassy, but he has no criminal record. I don't think he even had a parking fine.'

What is apparent is that Du went to his rival's luxury home and once inside, he carried out a savage crime that shocked the local community and police officers.

'There were two distinct sites of violence, one downstairs and one upstairs,' Timmins said. 'I think the main argument occurred between Mr Ding and Mr Du downstairs, then he killed the others as he encountered them in the house.

'This was a very violent attack and involved the use of a lot of force. What may be of some comfort is that it seems the victims died very, very quickly.'

All four bodies were found on Sunday evening inside their home in Pioneer Close. They all died from multiple stab wounds.

Chui, 47, is known to have grown up in Shanghai, where she studied chemical engineering. She moved to Britain and took a master's degree in physical chemistry at Southampton University, working as a researcher in the chemical industry before moving to Northampton with her husband in 1994. As well as her business ventures, she was working at her daughter Alice's secondary school, the Caroline Chisholm School, where she taught Putonghua classes.

Her husband, who had a stutter, had worked at Manchester Metropolitan University since 2004, a few years after arriving from Hangzhou , Zhejiang province.

Colleagues in the university's division of chemistry and environmental sciences described the 46-year-old as 'a very nice, gentle person, who loved his children'.

A Facebook page called the Jeff Ding Appreciation Society had been set up some years ago by grateful students. This week it became a place to pay tribute to a man many called a 'genius'.

Some of his present crop of students are hoping to show their support to the lecturer and his family by wearing a 'Jeff Ding jumper' for their coming exams or making a T-shirt with his catchphrases for their exams.

Eldest daughter Xing 'Nancy' Ding was said to be a 'stunningly talented' teenage girl. The 18-year-old had been deputy head girl at Northampton High School, where she was described as a wonderful pupil, and had been offered a place at university in Nottingham to study medicine this year. Her sister, Alice, 11, was described as a 'smiling, lively and curious' girl, who was also very talented, both academically and musically.

Stunned neighbours issued a statement that summed up their feelings in one sentence: 'A family with so much talent, and yet so much humility.'

Relatives of both families have been contacted in China, although none of the victims has been formally identified yet because they have no relatives in Britain. The university lecturer's brother in the United States and his elderly parents in Hangzhou are said to be deeply shocked by the news of his murder.

It also emerged that Du's wife had fled their home after dark while police hunted her husband. One neighbour, who did not want to be named, said: 'I did knock on their front door late last night and shouted through the letter box to see if his wife was all right but I didn't get any answer. I spoke to a few other neighbours and they said they saw Mrs Du coming out of the house carrying suitcases. I would imagine she has gone to stay with family for support.'

Before she fled, Dr Can Chen said: 'It is horrendous what has happened to this family. I do not know what is going on or where my husband is. I am so worried and so shocked that this has happened.'

She said the dispute over money had been 'very stressful', and claimed she and her husband did not get money she says was owed to them by the family.

'My husband has been in a very difficult place. He has been acting strangely. I'm not well at the moment,' she said.

Detectives have appealed to the large Chinese communities in Birmingham, Coventry and Northampton to help track down Du and a missing silver Vauxhall Corsa hire car that disappeared from outside the Ding's home at about the time of the killings.

But Timmins said some of the answers to this mystery might lie thousands of kilometres away in China. He said Interpol had been alerted.

'If Mr Du has gone back to China, he will go to people he knows, whether it's the same village, city or region,' Timmins said. 'He had enough money on him to survive, whether he is still in the UK or has returned home. He also crucially had two days' start on us before the bodies were discovered.

'If he is seen or someone hears about him, then those people need to inform the authorities. Whatever route that information comes back to us is not important, just as long as it comes back to us.'

Ultimately, Timmins said, it was not a matter of if but when Du was found. 'We are determined to invest a lot of time and effort in bringing him to justice, wherever he is.'

Price discrepancy

Victims Helen Chui and her husband tried to sell their house for GBP210,000

Their killer believed this was a ploy to get out of paying him, because the house should have been worth, in pounds: GBP275,000