Staffordshire Police launched an inquiry into the murder of amateur footballer Kevin Nunes, 20, who was gunned down in a country lane in 2002, British media reported.
Nunes, a drug dealer who had been on the books of Tottenham Hotspur, was shot dead in an execution style killing after a gang dispute.
His killers, Levi Walker, Antonio Christie, Adam Joof, Michael Osbourne and Owen Crooks were all jailed for life after being found guilty of murder by a jury at Leicester Crown Court.
The Independent Police Complaints Commission (IPCC) will look into the handling of the investigation into case of the four officers, including the lead on police ethics. Five men were jailed in connection with the killing in 2008.
The IPCC confirmed that formal notice of investigation had been served on “a number of former and serving Staffordshire Police officers”.
Meanwhile, Northamptonshire Police Authority confirmed that its force's chief constable Adrian Lee and deputy chief constable Suzette Davenport were being investigated.
Lee is also the head of the Association of Chief Police Officers' ethics portfolio.