It is exactly one year since Jifeng Ding, his wife Helen Chui and their two daughters were stabbed to death in their home in Wootton, Northampton.
The anniversary comes as police hunting for a man suspected of the killings have increased the reward for information which could lead to his arrest to £25,000.
Anxiang Du, who detectives named as the main suspect, has still not been traced.
Detective Chief Inspector Tom Davies said police were "unwavering" in their efforts to find Anxiang Du, and that they "strongly believe" he is still alive.
It was revealed that so far in the investigation, detectives have spoken to 2,000 people in connection with the case, and have gone through 5,000 hours of CCTV footage.
Police say there have also been 380 reported suspect sightings, in countries including France, Spain and Gibralter, but that so far none of them have been confirmed as Anxiang Du.