Police are increasing the reward for information about the murders of a family of four in Northamptonshire to £25,000.
Jifeng and Helen Ding and their two daughters, Alice, 12, and Xing, 18, were stabbed to death at their home in Wootton, in May last year.
Police have named Anxiang Du, who has not been traced, as the main suspect in the case.
Four people are on bail on suspicion of conspiracy to assist an offender.
Police investigating the murder of a family of four killed in their home in Northamptonshire are renewing their appeal to find the killer.
A close friend of a family stabbed to death in their home has criticised detectives saying more should have been done to catch their killer.