Three people have been arrested this morning in connection with the investigation into the deaths of a family-of-four in the county in April 2011.
A 54-year-old woman was arrested in Coventry, a 39-year-old woman was arrested in Gloucestershire and a 25-year-old man was arrested in London.
All three have been arrested on suspicion of conspiracy to assist an offender in connection with Operation Nene.
All three will be interviewed in local police stations to where they were arrested.
The arrests were made as part of a joint operation involving the local forces and the East Midlands Special Operations Unit Major Crime team.