A watchdog investigation into how police handled the controversial on the runs (OTRs) scheme for republican fugitives was unfair and unbalanced, a House of Commons committee has been told.
Peter Sheridan, a retired assistant chief constable of the Royal Ulster Constabulary (RUC) and Police Service of Northern Ireland (PSNI) claimed the report by the Police Ombudsman for Northern Ireland (PONI) had been rushed through with "hindsight bias".
Mr Sheridan said: "[The PONI report] lacked fairness, lacked balance and lacked thoroughness.
"As someone who has read hundreds of investigations the report is in my view written in a way that suggests that conclusions were arrived at first and then evidence to support the conclusions gathered and evidence to the contrary view received little weighting."
Mr Sheridan was giving evidence to the Northern Ireland Affairs Select Committee which is holding an inquiry into government letters sent to more than 200 republican paramilitary suspects.
He told MPs he would think twice before engaging with the ombudsman or encouraging other former officers to co-operate with his office again.
He added: "I say this with considerable regret. I have always been a champion of the role of Police Ombudsman in Northern Ireland, even to the extent of encouraging ex-officers to cooperate with PONI investigations. But in this case my own confidence has been knocked. I approached requests for interviews from PONI in a very open and willing way but my experience has meant I am likely to approach any such requests differently in the future."
Ombudsman Dr Michael Maguire examined the PSNI's role in the contentious OTR scheme - established by the Government at the request of Sinn Fein - and in particular officers' handling of the case of John Downey, who walked free from the Old Bailey earlier this year when his prosecution for the murders of four soldiers in the IRA's 1982 bomb in Hyde Park collapsed when it emerged he had been mistakenly assured in an official letter that he was able to return to the UK.
The PSNI was heavily criticised for failing to inform the authorities issuing the letter that Downey was wanted by the Metropolitan Police for questioning over the Hyde Park outrage.
Downey, 62, from Co Donegal, denied involvement in the attack.
The error, and subsequent missed opportunities to correct it, happened in the period from 2007 to 2009.
The PSNI had been assessing evidence in individual cases as part of the process since 2000 but in 2007 it initiated a fresh drive to complete the task - called Operation Rapid - after the Government signalled a desire for it to be sorted out.
The fresh impetus from the Labour administration came in the politically-sensitive period before devolution was restored to Stormont.
Dr Maguire said Operation Rapid lacked clarity, structure and leadership and claimed there was disjointed communication between key officers.
Mr Sheridan, who retired from the PSNI in 2008, also told MPs he had had been uncomfortable briefing senior Sinn Fein members including Gerry Adams and Gerry Kelly about republican terror suspects whose status had changed from wanted to not wanted.
He said: "It was an extraordinary thing that we were being asked to do and none of us were comfortable with it."
Asked by North Antrim MP Ian Paisley who was to blame for the OTR debacle, Mr Sheridan told the committee he did not believe there had been a conspiracy.
He said: "I don't think anybody set out at the time to create these circumstances.
"Because it wasn't designed at the time and set down in policy and structure, it kind of ambled along and people then made their own bits to it.
"Did the lie get bigger - I don't know whether there was a lie in it but the problem got bigger...Once you start to change the system and you contaminate it that way, it leaves it open for errors and that's what happened in this."
Household Cavalry Lieutenant Anthony "Denis" Daly, 23, died in the Hyde Park explosion on July 20 1982 alongside Trooper Simon Tipper, 19, Lance Corporal Jeffrey Young, 19, and 36-year-old Squadron Quartermaster Corporal Roy Bright.
A judge-led review of the wider letters scheme ordered by Prime Minister David Cameron and published in the summer found it was systematically flawed in operation but not unlawful in principle.
Meanwhile, Kate Hoey, MP for Vauxhall, claimed the Secretary of State for Northern Ireland did not want the senior civil servant who signed off John Downey's letter informing him he was no longer wanted, to attend the committee.
She said: "The Secretary of State is trying to stop him coming before this committee."
In his evidence to the committee, Dr Maguire defended the integrity of his report which was undertaken after a request from the PSNI chief constable.
He said: "I don't think I have been unfair to Mr Sheridan...
"I cannot look at the NIO; I cannot look at the PPS (Public Prosecution Service); I cannot look at any other agency involved in this. My remit is exclusively on police.
"We can't get away from the fact that there was a mistake. And, whenever the opportunity was given to correct that mistake it wasn't taken."