Ch Insp Darren Wareing, who is in charge of the North Wales Police roads policing unit, said many people did not realise they could still be over the limit the next morning after a drinking session.
Det Ch Supt Kier Pritchard, head of protective services at Wiltshire Police, said that while the charge had never been put in court, "it is very much our intention to continue the live murder investigation and bring that final closure for Becky's family".