The relatives of four people murdered after alleged security force collusion with loyalist paramilitaries in Northern Ireland are suing the police.
The families' solicitors issued a writ to Chief Constable Sir Hugh Orde in Belfast today.
A report last month by Police Ombudsman Nuala O'Loan found officers from the Royal Ulster Constabulary Special Branch had protected their agent from prosecution for his part in 16 Ulster Volunteer Force murders in north Belfast between 1991 and 2003.
Andrea Murphy, deputy director at Relatives for Justice, is supporting their case.
She said: "They had no idea that the deaths of their loved ones could have been prevented and that there was such a high level of involvement in the killings."
The families of Sharon McKenna, Peter McTasney, Gerard Brady and John Harbinson are taking the action.
They are claiming negligence, breach of statutory duty, conspiracy to injure, assault, trespass against the person and misuse of power in public office.
PA