The Ding family was found stabbed to death Northamptonshire Police has named Anxiang Du, 52, from Coventry, as the key suspect and believe he has assistance and is hiding in London.
The case will feature on Crimewatch on BBC1 on 24 May.
The murder investigation moved to London when the family's missing Vauxhall Corsa hire car was found in St John's Wood.
Police believe Mr Ding, a lecturer at Manchester Metropolitan University, and his family were killed on 29 April. Their bodies were found two days later.
CCTV images have been released showing Mr Du, at Northampton Bus Station on the day of the murder.
Mr Du, who worked at a herbal medicine shop in Birmingham, went missing a day after losing what has been described as a bitter court battle over his shared business interests with the Ding family.
Last week it was revealed that a 999 call believed to have been made as the family was being murdered was being investigated by the police watchdog.
Northamptonshire Police said it had referred the response to an abandoned 999 call on 29 April to the Independent Police Complaints Commission.
Crimestoppers has put up a £10,000 reward to find the person responsible for murdering the family.
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