The PSNI chief constable has said he was obliged under law to investigate the suspected theft of documents from the Police Ombudsman.
Documentary makers Barry McCaffrey and Trevor Birney were detained by a force brought in from outside Northern Ireland in a bid to boost public confidence.
George Hamilton admitted he was uncomfortable with arresting journalists.
He said he had read a statement of complaint from the Ombudsman about the theft.
“Our actions have been lawful and proportionate.
“It is not a comfortable place to arrest journalists but we have an obligation under the law.
“We had a positive obligation to investigate but we did have a statement of complaint, I have read it myself.”
Mr Hamilton told the Policing Board: “I want to bust the myth that there was no statement of complaint, we had a report of what was quite a serious offence in terms of theft of the documents.”
Mr Hamilton said he had asked Durham police to carry out the investigation to give confidence.
He said the Chief Constable of Durham Constabulary is willing to attend a meeting of the Policing Board to answer questions around the arrests.
The confidential documents surrounded a police investigation into the loyalist murder of six men at a pub in Loughinisland in Co Down.
Mr McCaffrey and Mr Birney produced a documentary about the 1994 killings.
The No Stone Unturned programme examined claims of state collusion in the murders.