The grieving relatives of a university lecturer stabbed to death along with his wife and two children say they believe that justice will prevail in the hunt for the killer. Hangzhou -born Dr Jeff Ding Jifeng, 46, his 47-year-old wife, Helen Chui, and their daughters, Nancy, 18, and Alice, 11, were murdered in their luxury home near Northampton in the Midlands of England on April 29. The couple's former friend and business partner, Du Anxiang, disappeared after the killings and is still the only suspect that police have in their hunt for the killer. Police believe the 52-year-old fugitive is being shielded, possibly by contacts in Britain or his native China, and they have appealed to his family and friends in Hunan province for help. On Sunday, Jeff Ding's brother, Ding Jixiang, said he couldn't bear to hear the name of the man suspected of the brutal killings. Ding Jixiang, a biology professor from Kentucky, US, was in Britain to help police in the hunt for Du. 'The person who did this is brutal. Absolutely brutal,' he said. 'I think these kinds of things are just beyond my imagination, and I believe beyond the imagination of any human being. 'For a long time, even now, I didn't want to hear [Du's] name. But if he really did it, I have many, many, many questions to ask him. I want to ask him how he could stab a knife into an innocent girl's heart, not once but twice? How could you do that? An innocent girl. I also want to know what he was feeling, or whether he had any feelings, when he saw the girls' expressions.' Du and Jeff Ding had been running Chinese herbal shops together in Northampton and Birmingham. But the relationship soured over their business dealings, and the two families were embroiled in a string of court proceedings that culminated in Du's assets being frozen on the evening of April 28. The family was found dead the next day. Police believe Du travelled from his home in Coventry to his herbal medicine shop in Birmingham, then to the family's home in the village of Wootton, near Northampton, committed the murders and took his former associate's car. The investigation took detectives to London, where the car was found abandoned in a street. But despite concentrating their efforts on the British capital's Chinatown, officers have hit a wall of silence and mistrust. Jeff Ding was a science lecturer at Manchester Metropolitan University. His brother said he found out about the killings online. 'I was completely shocked,' Ding Jixiang said. 'I could not finish the news story once I saw the pictures. I could not believe that four people were gone. I mean, it is just a complete shock. 'And then I thought about my parents. They lost their children and their grandchildren in one day. 'The first thing I did was call a relative, my mother's cousin, in our hometown in China, and asked them to go to stay with my parents, that is the only favour I wanted. For Helen's parents and my parents, the impact could be fatal.' For his family, he fears, 'The impact ... will be just too much.' Asked if he believed the killer would be brought to justice, he said: 'Sooner or later. It is a matter of time. That is what I believe.' Zhu Li, Helen Chui's sister-in-law, who lives in China, said: 'Not only has the murderer killed our two family members, but he has also taken away the lives of two lovely children. The way that the murderer carried out the killings, and their brutality, has shocked the world.'