Police investigating the murder of a family of four have 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, 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.