Analysis: HET boss Dave Cox steps down step down from his role
There were heated exchanges last week in a private meeting between the Chief Constable Matt Baggott and board members when he set out his proposals for the future of the Historical Enquiries Team (HET).
While Mr Baggott said a new HET leadership team would be in place by 28 September, he added that the director of the team, Dave Cox, would stay in his job until the end of December.
They disagreed and said he should step down at the end of this month, when the new leadership team takes control.
The BBC has seen letters which reveal that the board and the chief constable have been at loggerheads since the government's national policing watchdog, Her Majesty's Inspectorate of Constabulary, published a highly critical report about the HET in early July.
The letters chart a power struggle about who should take the lead in responding to that report.
On the 5 August Brice Dickson, the chairman of a working group the board set up to review the future of the HET, wrote to Matt Baggott about a meeting they'd held four days earlier.
He said the chief constable had accepted all of the recommendations in the inspection report, and had "agreed that the Board is leading on the implementation" of its recommendations.
The letter also stated that Matt Baggott had agreed to submit his proposed action plan to the working group for its "consideration and approval".
But in a response four days later, the chief constable said he was "legally unable to agree to the board leading on the implementation" of the report, because it was an operational matter falling solely to himself.
The letter included a proposed action plan, which said Dave Cox would retire on the 31 December - and that a new leadership team would be put in place.
But the Policing Board made it clear it wasn't happy.
In a response, Mr Dickson said: "For the benefit of clarity, the proposals in the paper forwarded have not been approved at this time by the board. "
He added: "Given its lead role, I hope you will respect the Policing Board's position."
After a meeting between the chief constable and the group on Thursday, both sides issued a joint statement saying the new exit date for Mr Cox would be 28 September.