Mercer, 50, was bludgeoned to death in West Molesey, Surrey, on March 14 and found dead at the end of her driveway.
A 24-year-old woman from Kent was arrested yesterday on suspicion of assisting an offender. She has been bailed until January.
"Pursue all potential leads"
Inspector Paddy Mayers of Surrey’s major crime team said the arrest was “carried out to establish if there is any new evidence which could help to identify those who committed the brutal attack on Robyn. We will continue to pursue all potential leads and will relentlessly carry on until those responsible are behind bars".
Five people remain on bail in relation to the murder investigation, called Operation Zebu, including two 26-year-old men from West Molesey who were arrested on suspicion of conspiracy to burgle and murder. They have been re-bailed until next week.
Mercer was a silver specialist at Mason's Yard's JH Bourdon-Smith.
