Jifeng Ding family murder police increase reward to £25,000 Police investigating the murder of a family of four today increased a reward for information leading to the prime suspect's arrest to £25,000. Detectives hunting Chinese businessman Anxiang Du, 52, raised the reward from £10,000 almost 12 months since university lecturer Jifeng Ding, his wife Helen Chui and their two daughters Alice, 12, and Xing, 18, were found stabbed to death at their home in Wootton, Northampton on May 1 last year. Detective Chief Inspector Tom Davies said a national manhunt was continuing, but the search for Du - who has not been seen since the day of the murders - had spread internationally with the help of Interpol and the Serious Organised Crime Agency (Soca). The family were murdered on April 29 last year and as part of an anniversary press conference at Northamptonshire Police headquarters today, Mr Davies said he hoped the substantial reward would bring new information direct to the police. "I certainly feel that this is an appropriate time to increase the sum of money offered to ensure that we take every opportunity to elicit that vital piece of info which will allow us to identify where he currently is," he said. Du, 53, from Coventry in the West Midlands, was declared the only suspect soon after the discovery of the murders. Mr Davies told the press conference: "I strongly believe that Mr Du is still alive and is being assisted by associates or friends. I accept he may have left the UK fairly soon after the murders and we're working with Soca, Interpol, and other law enforcement agencies to ensure that the appropriate measures are in place to identify and alert the police should he attempt to travel across borders. Initial inquiries into the murders focused on key areas including Northampton - where the murders were committed, the West Midlands - where the suspect was from - and London - where it is believed he travelled to and abandoned the car. Mr Davies said the Ding family had been in the UK since the late 1990s. Mr Ding worked as a lecturer at Manchester University and his wife worked locally at a school in Northampton. Since around 2002 Mr and Mrs Ding had been involved in a civil dispute with a Chinese family over a business issue. To date there has not been one confirmed sighting of Du, who is a qualified doctor of Chinese medicine and speaks English and Mandarin, anywhere in the world. Recent developments in the case saw the arrest of four people last week, on suspicion of conspiracy to assist an offender. They were all released on bail pending further inquiries. Mr Davies said: "We have recently made a series of arrests in respect of the investigation, for operational reasons I cannot comment any more on those arrests. What I can say is that we will continue to work tirelessly to locate and arrest Anxiang Du. Northamptonshire Police is working with 43 police forces nationwide and through Interpol have accessed and are in touch with 180 countries worldwide. There have been more than 2000 people visited and interviewed regarding sightings, information, intelligence and questioning. There has been more than 5,000 hours of CCTV seized from around the UK. In addition, there have been more than 380 suspect sightings, as well as nine arrests for various offences, some of whom were arrested in the belief that they were the suspect. Mr Davies added: "I have to accept Anxiang Du may have left the UK. Someone must have assisted him and is likely to still be assisting him or aware of where he is. On March 25, three officers travelled to China to speak to associates of the suspect for any information they may have in identifying people who could have assisted him in his escape. They also met the family of the victims and updated them on the investigation. Anyone with any information relating to Anxiang Du or to the inquiry is asked to contact Crimestoppers anonymously on 0800 555 111 or the police on 101.