The police ombudsman in Northern Ireland has launched an investigation into allegations of collusion between the police and senior members of the Ulster Volunteer Force in the Shankill Road area of Belfast.
A team has been established to examine why there have not been charges or convictions in a number of high-profile murders.
The most recent killing being investigated was that of Bobby Moffett who was shot dead in May 2010 after a dispute with a senior figure within the UVF.
The International Monitoring Commission said the murder of the former loyalist prisoner was sanctioned by UVF leaders from the Shankill.
Ombudsman Michael Maguire's office confirmed he is examining allegations that police failed to properly investigate a series of fatal shootings in north and west Belfast between 1989 and 2010.
It is believed investigators will examine claims that no one has been charged or convicted in connection with the murders because informers were being protected.
The police said: "PSNI are involved in a major investigation into criminality in north and west Belfast involving the UVF which stretches back over a considerable period of time and which runs parallel to the ombudsman investigation Operation Stafford.
"With regard to the investigation into the murder of Bobby Moffett, this remains a live investigation into which police have committed very considerable resources and gone to substantial length to bring charges.
"PSNI has left no stone unturned in the Moffett investigation and is greatly frustrated that it has not been able, thus far, to bring charges of murder against those involved."