A former police inspector tonight denied involvement in the notorious killing of the anti-racist protester Blair Peach, after a report released earlier in the day suggested he may have been the officer who struck the "fatal blow".

Alan Murray, who is now a university lecturer but was a 29-year-old Metropolitan police inspector in 1979, said he was the victim of a bungled investigation into Peach's death. "I did not kill Blair Peach. Of that I am certain," he said.

Murray was speaking after the release of more than 3,000 previously secret documents that shed new light on the death of Peach, a 33-year-old teacher from New Zealand whose skull was crushed by a single blow to the head during a protest against the National Front in Southall, west London, on the evening of 23 April 1979.

The documents appeared to confirm the long-held suspicion that Peach was likely to have been killed by an officer from the Met's riot squad, the special patrol group (SPG).

The key document was produced by Commander John Cass, who ran the Met's internal complaints bureau and led the inquiry into Peach's death. He concluded that Peach was "almost certainly" killed by one of six SPG officers, some of whom then lied to cover up the actions of their colleague.

No officers were ever charged over Peach's death, although the event marked one of the darkest moments in Scotland Yard's history. Sir Paul Stephenson, the Metropolitan police commissioner, recognised as much when he said the report made "uncomfortable reading". He unequivocally accepted the finding that a Met officer was likely to have been responsible for the death and, in an unusual move, expressed his regret.

"I have to say, really, that I am sorry that in over 31 years since Blair Peach's death we have been unable to provide his family and friends with the definitive answer regarding the terrible circumstances in which he met his death," he said.

Asked if he was apologising for the death of Peach, he replied: "I am sorry that officers behaved that way, according to Mr Cass."

Murray, who retired from the Met soon after the death and now lectures in corporate social responsibility at Sheffield University, was not named in the documents that were made public. But he accepted that from evidence given at Peach's inquest and other material, he was easily identifiable. The former inspector is among dozens of police officers questioned over the death more than 30 years ago who can now be identified.

They include Tony Lake, who attended the Southall demonstration as an SPG sergeant, and later rose through the highest ranks of the constabulary, becoming the chief constable of Lincolnshire police.

Lake, who once chaired the national DNA database and was awarded an OBE when he retired two years ago, declined to comment last night on Peach's death but said that a 1981 newspaper report linking him to the officers identified in the Cass report was "fundamentally wrong".

The Met agreed to release the documents last year in the aftermath of the death of Ian Tomlinson, a 47-year-old newspaper seller who died after being attacked by police at the G20 protests in London. The officer filmed striking Tomlinson was a member of the territorial support group, which replaced the disbanded SPG in 1987. The Crown Prosecution Service is still considering whether to charge the officer with manslaughter.

Yesterday's publication marked the culmination of a 31-year campaign by friends and family of Peach for full disclosure of the Met's inquiry into the death. The Cass report was suppressed in 1980 by the late Dr John Burton, the coroner who oversaw the inquest into Peach's death.

The inquest controversially returned a verdict of "death by misadventure", but recently disclosed documents suggest Burton was biased in favour of the police. He wrote to ministers before the end of the inquest, dismissing the belief that Peach was killed by an officer as political "fabrication".

After the inquest, Burton penned an "unpublished story" about the Peach death which railed against what the coroner saw as a leftwing campaign to destabilise the legal establishment. Senior civil servants managed to persuade him not to publish his account. One official wrote: "An article like this would be a heaven-sent opportunity to those who wish to get maximum publicity out of this incident to argue that the coroner was biased and for this reason the inquest was unsound."

Peach's long-term partner, Celia Stubbs, said yesterday she felt totally vindicated by the Cass report. She described its released as "the beginning of the end" of her campaign for answers.

She repeated her long-held belief that Peach would not have wanted to be known as a political martyr, but accepted that the search for answers over his death had for many become a political cause in itself, galvanising concern over what were considered the brutal actions of corrupt and unaccountable police.

When Peach's body was finally buried – 51 days after his death – thousands of activists marched across London. Around 8,000 mainly Sikhs from Southall had already paid their respects at his open coffin, which lay in a nearby theatre the previous night.

The suspicions of most of those mourners – that a police officer killed Peach – were all but confirmed in yesterday's report.

Stubbs said: "It is fantastic after 31 years. I have only read 200 pages of the report but I feel that we have really been vindicated because we have always said that Blair had been killed by a policeman. It says in the report that it was an officer that struck Blair.

"I never really expected a prosecution. I don't regret that, I am just pleased that we have the report so we can see what happened on the day."

The Cass report was written at the end of the summer of 1979, following months of inquiries.

In laying out his terms of reference he said: "My brief is to investigate the circumstances surrounding the death, so I do not propose to enlarge much further on the events of that day except to emphasise that it was an extremely violent volatile and ugly situation where there was serious disturbance by what can be classed as a 'rebellious crowd'.

"The legal definition 'unlawful assembly' is justified and the event should be viewed with that kind of atmosphere prevailing. Without condoning the death I refer to Archbold [Criminal Pleading, Evidence and Practice] 38th edition para 2528: "In case of riot or rebellious assembly the officers endeavouring to disperse the riot are justified in killing them at common law if the riot cannot otherwise be suppressed."

If Cass was seeking to exonerate his men, it was an endeavour he found difficult in the face of more than 3,000 pages of witness testimony, forensic evidence and tense interviews with officers. After reviewing hundreds of pages of evidence, he reached his conclusion: that it could "reasonably be concluded that a police officer struck the fatal blow". Despite this, he said there was insufficient evidence to bring charges of unlawful killing.

Cass had narrowed his investigation down to six SPG officers in carrier U11, the first vehicle to arrive in Beachcroft Avenue, the suburban street where Peach was found stumbling around, barely able to talk. Moments earlier, 14 witnesses had seen "a police officer hit the deceased on the head" but, according to Cass, there were discrepancies in their evidence and most could not identify an officer from repeated identity parades.

Although he did not recommend charges over the death, Cass did name three officers he proposed should be prosecuted for perverting the course of justice, believing they had lied to his investigators to cover up the actions of their colleague.

Analysing their statements, he found some had been engaged in a "deliberate attempt to conceal the presence of the carrier at the scene at that time".

In a key passage, he wrote: "It is now clear that [carrier] U11 was at the scene and almost certainly the officer who struck the blow had come from that carrier. It will be appreciated that the explanation given by the crew of the carrier would be of paramount importance to the investigation." He went on to express concern over the "attitude and untruthfulness" of some of the officers in the van, and found their responses "seriously lacking".

His recommendation that three officers be prosecuted for lying to their seniors was apparently overruled by the then director of public prosecutions, Sir Thomas Hetherington, who within weeks of receiving the Cass report announced there was insufficient evidence to bring any charge against any officer. After the Met reviewed the conduct of the officers, it was felt that none should be disciplined.

Of the six SPG officers, Cass said there was an "indication" that one officer in particular – the first to emerge from the carrier – struck the "fatal blow", but emphasised that there was "no evidence of a conclusive nature". The name of that officer was redacted from today's published version of the report, but last night Murray acknowledged that it was a reference to him. He accepted he was the first out of the van and said he was aware at the time that Cass had made him a "prime suspect" in the inquiry. But he criticised the investigation, and accused Cass of turning to him in the absence of more concrete evidence.

"In a report like that, that man [Cass] can write anything he likes," he said. "So he is pursuing me and trying to fit me up for a murder that I didn't commit, and then he tells people that I am stressed."

Claiming he had been a "hostage to fortune", Murray accused Cass of bungling the investigation.

Cass, 85, who retired 20 years ago, said last night he was unwilling to comment on the allegations being made by Murray. But the Met stood by Cass, saying his findings were the result of an extensive and robust inquiry. Commander Mark Simmons, the officer who now runs the Met's complaints department and oversaw the release of his predecessor's report, said "a significant amount of resources" had been put into the investigation. "I've got no reason to disagree with Commander Cass's conclusions," he added.

Cass's findings were also welcomed yesterday by Deborah Coles, a co-director of Inquest, an organisation that was set up in 1981 partly in response to Peach's death and provides advice on contentious deaths. However, she raised questions about the institutions that hold police to account. "The whole police investigation into what happened on 23 April 1979 was clearly designed as an exercise in managing the fallout from the events of that iconic day in Southall, to exonerate police violence in the face of legitimate public protest," she said. "The echoes of that exercise sound across the decades to the events of the G20 protest and the death of Ian Tomlinson in 2009."

The history

April 23 1979 Blair Peach dies at a protest against the National Front in London. Scotland Yard announces an investigation and interrogates police officers. It finds 14 witnesses who say they saw Peach attacked by a police officer. In July, tens of thousands attend Peach's funeral.

October 1979 After reviewing the Metropolitan police's internal investigation, the director of public prosecutions, Sir Thomas Hetherington, says there is insufficient evidence to charge any officer. We now know that the Met inquiry, by Commander John Cass, said three officers should be charged with perverting the course of justice.

May 1980 An inquest into Peach's death returns a verdict of death by misadventure. Campaigners accuse the coroner, Dr John Burton, of being biased in favour of police and leaning on the jury. Burton refused lawyers acting on behalf of Peach's friends and family access to the Cass report.

July 1988 In an out of court settlement, the Met agrees to pay Peach's relatives in New Zealand £75,000 in compensation. His partner Celia Stubbs was not entitled to a payout.

April 2009 Newspaper seller Ian Tomlinson dies during G20 protests in London after being struck by police. Parallels are drawn with Peach's death. A motion is put to Scotland Yard's watchdog for release of the Cass report, which is published almost a year later.