One of Scotland's most senior police officers has admitted the force failed four colleagues at the centre of a probe into illegal surveillance.
Deputy Chief Constable Rose Fitzpatrick said she continued to offer her "wholehearted" apology to the serving and retired officers who were targeted by Police Scotland's Counter Corruption Unit (CCU).
However she defended the force's handling of an independent investigation into the CCU carried out by Durham Constabulary.
The external force was asked by Police Scotland to probe the CCU after it emerged that guidelines on accessing communications data were breached in 2015 by officers attempting to uncover a journalist's sources in relation to the murder of Emma Caldwell in 2005.
Michael Barton, Chief Constable of Durham Constabulary, last month told Holyrood's Justice Sub-Committee on Policing the four complainants had been "gravely wronged" and said he had been prevented from carrying out a proper investigation into the CCU.
Ms Fitzpatrick said she had met with three of the four wronged officers in March of last year to offer a "wholehearted and unreserved" apology, and had also apologised to all four by letter "not only the failings which occurred in 2015 but for the subsequent impact on them and their families".
She said: "As I said to them when I met them and I have repeated in my letters to them, I feel we failed them as an organisation absolutely and that we continued to fail them by not being in contact with them and I continue to offer them my wholehearted apologies for that failing."
Mr Barton told the committee he had originally been asked to carry out an investigation into the CCU following a ruling of the Investigatory Powers Tribunal (IPT) but that was later downgraded to an inquiry.
Ms Fitzpatrick acknowledged there had been a "significant difference of professional view" between the two about how to proceed but that had been resolved by her having taken legal advice.
She said: "It's not unusual in complex matters for there to be a difference of professional view about the best way of progressing things.
"But we were very clear that he and Durham Constabulary had been asked to undertake an independent investigation only into the complaints allegations, the non-criminal complaints allegations, and that our conduct regulations require other stages to take place should there require to be an investigation then into the conduct of individual officers."
Earlier this year an independent investigation into allegations of misconduct against officers in the former CCU, carried out by the Police Service of Northern Ireland (PSNI), found there had been no misconduct.