Five police officers have been disciplined after an arson attack at a GAA club was wrongly blamed on an electrical fault.
An examination by the Police Ombudsman found that officers failed to properly investigate the crime at the Sean Dolan clubhouse in Londonderry in December 2011.
Dr Michael Maguire particularly highlighted a failure by police to note a number of figures and flashing lights in CCTV footage of the incident.
"The initial investigation lacked leadership, direction and supervision," he said.
A senior member of the Derry-based club told the ombudsman's office that in the wake of the fire he met two police officers and Fire Service investigators at the scene, who told him there had been no sign of a forced entry and that the fire may have been caused by an electrical fault.
The next day he said a constable and Fire Service investigators told him they were almost definite the fire had been caused by an electrical fault and that there was no indication of a crime.
The club member said the police officer contacted him later that day and, having watched the footage from the CCTV cameras in the clubhouse, reiterated his view that the premises had not been deliberately set on fire.
The police later issued a press release stating that the cause of the fire was not suspicious.
Two members of the club subsequently collected the CCTV footage from police and said that within five minutes of looking at it they observed "shadowy figures" and a number of bright flashes from within the building.
They then contacted members of Sinn Fein, who arranged a meeting with senior police officers, and together they viewed the footage.
The following day police issued a fresh public statement indicating they were now treating the fire as arson.
A new detective sergeant was appointed to re-investigate the incident.
Probing concerns about the initial police investigation, a team from the ombudsman's office visited the scene, watched the CCTV footage, examined all relevant police documentation and spoke to police officers, fire service officers and members of the club.
The detective sergeant who had initially been assigned to the case told the ombudsman's investigators he had relied on the opinion of the Fire Service investigators to "point him in the right direction" and could not recall suggesting to club members that the fire had been caused by an electrical fault.
Dr Maguire said the officer claimed that when he viewed the CCTV footage, he did so for a matter of minutes on a small screen and said the picture quality was not good.
The officer confirmed that he did see "flickering" but said he thought this was caused by a car indicator light or something similar.
The detective sergeant said he did not conduct door-to-door enquiries, did not check the perimeter of the clubhouse and did not notice a roof tile which had been removed.
He then appointed the constable to continue the investigation.
The constable had just been seconded to the Criminal Investigations Department and told the ombudsman's investigators he had no experience of such incidents and claimed he received little or no guidance from the detective sergeant or more experienced officers.
This officer said he watched the CCTV footage in its entirety but focused mainly on the upstairs area of the clubhouse after staff had left.
The constable admitted he did not show the Fire Service investigators all of the footage in his possession and that he failed to conduct a number of other enquiries before he deemed the fire not to be suspicious.
Dr Maguire said investigators from the Fire Service were also interviewed.
One of them said that on the basis of the material shown to them by the PSNI, which they believed was all the relevant footage, they concluded that the fire had been intense and was most likely caused by an electrical fault, as there was no evidence to suggest otherwise.
The ombudsman team also spoke to the Crime Scene Investigator who attended the blaze.
She said the area could not be properly examined, but said there were no signs of a forced entry or smell of petrol.
The CSI said she and the constable initially watched the CCTV on a small monitor which had a number of small windows, each showing footage from different parts of the premises.
She said that two or three minutes in, they saw a flash and a flame coming down from the ceiling and concluded the most probable cause of the fire was an electrical fault started in the roof space.
Dr Maguire recommended that the detective sergeant and the seconded constable be disciplined for their failure to investigate the fire properly and that a duty sergeant and two detective inspectors also face discipline for their failure to supervise and guide the investigation.
"Police failed to conduct basic investigative enquiries such as checking the perimeter of the club house, conducting house to house enquiries, thoroughly examining the CCTV footage or seeking to speak to the 999 caller who reported the fire," he said.
"The detective sergeant initially assigned as the investigating officer had no previous experience in attending a fire of this scale and the constable who he appointed to continue the investigation had minimal experience.
"Together they received insufficient guidance and assistance from more experienced officers."
A Police Service of Northern Ireland (PSNI) spokeswoman said: "In the early hours of December 28 2011, a fire destroyed the Sean Dolan GAA clubhouse at Creggan Estate in Derry.
"On January 3 2012, the Chief Constable (Matt Baggott) referred concerns about the effectiveness of the initial investigation to the office of the Police Ombudsman for Northern Ireland.
"We acknowledge that the PONI report identified a number of errors during the initial police examination and that there were failures on the part of five officers.
"The five officers were recommended for misconduct proceedings and this has been acted upon.
"A number of steps were taken by police following the incident. These included the appointment of an experienced detective chief inspector to ensure resilience at all levels of command.
"A CID support team was brought into the district for six months to allow coaching and training. Bespoke local training was delivered across a range of specific topics."