An investigation into alleged media leaks on police inquiries into the Castlereagh break-in and Stormont spy-ring has been established by the Chief Constable, Mr Hugh Orde.
The Police Service of Northern Ireland has declined to comment on reports that a senior Special Branch officer has taken early retirement because of the inquiry. A spokesman said the PSNI did not comment "on matters of personnel".
Some of the Special Branch officer's colleagues are said to believe his departure is being used as a concession to encourage Sinn Féin to join the North's Policing Board.
It is understood the investigation will be carried out by officers from outside the PSNI.
The controversy surrounding an alleged Provisional IRA spy ring at Stormont led to the collapse of the North's Executive and Assembly.
Last month, the PSNI raided Sinn Féin's offices at Parliament Buildings, Stormont. Four people, including a senior Sinn Féin official, Mr Denis Donaldson, have been charged in connection with the operation.