By Amanda Ferguson

BELFAST (Reuters) - The collusion of police officers was a significant feature in the 1994 killing of six soccer fans in one of the most notorious episodes of Northern Ireland's 'Troubles', a report by the province's police ombudsman said on Thursday.

The report is the latest to indicate state collusion in some of the 3,600 murders committed during the 30-year armed conflict between Catholic Irish nationalists seeking a united Ireland and their Protestant rivals who want to keep Northern Ireland British.

On June 18, 1994, Protestant paramilitary gunmen entered the Heights Bar in the village of Loughinisland and opened fire indiscriminately on customers watching Ireland play Italy in a televised World Cup match, killing six, including 87-year-old Barney Greene, one of the oldest victims in the 'Troubles'.

Among the failings identified, the report found that police informants at the most senior level within armed Loyalist groups were involved in the importation of arms used in at least 70 murders and attempted murders, including the 'Loughinisland massacre'.

Special Branch officers in the Protestant-dominated Royal Ulster Constabulary (RUC), which has since been replaced by a new force under the terms of a 1998 peace deal, failed to pass on intelligence relating to the informants' gunrunning, the report found.

It also listed a number of fundamental failings in the murder investigation, including the forensic strategy, enquiries around the getaway car and those connected to it, and in the strategy for making arrests and finding witnesses. 

"The protection of informants through wilful acts and the passive turning a blind eye; fundamental failures in the initial police investigation and the destruction of police records, are in themselves evidence of collusion," Police Ombudsman Michael Maguire said in the report.

"When viewed collectively, I have no hesitation in saying collusion was a significant feature of the Loughinisland murders."

The report found no evidence that security forces were aware the Ulster Volunteer Force (UVF), the most lethal Protestant paramilitary gang, were planning the attack but Maguire said the police approach to informants was a concern which appeared time and time again throughout the investigation.

The RUC, which the report said did not have the checks and balances in relation to the handling of informants that now exists in modern policing, requested guidance from the British government, but none was forthcoming, the report added.

Thursday's report was the second investigation into the Loughinisland killings after a 2011 report was rejected by families of the murdered men as a whitewash.

(Editing by Padraic Halpin and Gareth Jones)