Detective Superintendent Steve Fulcher 'had a lot to offer the police service', the Police Superintendents' Association of England and Wales have said.
The detective, who resigned from Wiltshire Police today, was the lead investigator in the Sian O'Callaghan murder enquiry in March 2011.
He was found guilty of misconduct in relation to breaches of the Police and Criminal Evidence Act when questioning the 22-year-old's killer Chris Halliwell in unorthodox interviews at Barbury Castle and Uffington, including not cautioning the mini-cab driver.
DSI Fulcher, who was a highly experienced officer in homicide investigations, was also found to have gone against force orders in releasing too much information to the media.
Eamonn Caroll, assistant secretary of the PSAEW, said: "The Police Superintendents' Association is aware of the decision of DSI Steve Fulcher to resign from Wiltshire Police. The association supported Steve Fulcher when he was under investigation by the Independent Police Complaints Commission and at his subsequent disciplinary hearing.
"He was a dedicated police officer who had a lot to offer the police service. In light of his decision, we wish him well for the future."