The head of the civil service, Sir Bruce Robinson, defended his decision not to dismiss a senior civil servant found to have interfered in the political process, on 29 June 2011.
Paul Priestly was suspended from his role as permanent secretary of the Department of Regional Development for helping to draft a letter of complaint to the Public Accounts Committee.
The committee had been investigating the department's handling of Northern Ireland Water.
Mr Priestly was subsequently downgraded to principal secretary.
Committee chair Paul Maskey of Sinn Fein said its investigation into the Northern Ireland Water issue became a shambles after the letter was received by members of the committee on 5 July 2010.
Sir Bruce explained his approach to the setting-up of the subsequent investigation led by Sir John Shortridge and that he understood the committee had agreed the report would not be made public.
Mr Maskey said he believed "the accountability mechanisms not only of the public accounts committee but of the entire assembly executive have been undermined with Mr Priestly's actions."
The SDLP's John Dallat drew attention to the deletion of the letter from the civil service computer system and commented that the Information Commission would regard this as "criminal activity".
Mitchel McLaughlin of Sinn Fein said, "this was quite clearly an attempt by one of the most senior civil servants to interfere with the political process."
He asked if it was not a matter of gross misconduct.
Referring to the matter of deleted email, Sir Bruce said the civil service computer system would "fall over" if there was not a requirement to delete.
The UUP's Ross Hussey was unhappy with Sir Bruce's briefing. "Nothing here has been transparent," Mr Hussey said.
"Nobody is accountable to us as far as I can see," he added.
Sir Bruce said he was as upset as the committee that this had happened.
In a discussion following the briefing from Sir Bruce, Mitchel McLaughlin said it was clear that a charge of gross misconduct, which could have led to dismissal, was ruled out from the beginning.
The committee then considered the matter of a letter of apology received from Paul Priestly. They voted to reject the letter.