A cold-case police team wanted to question Martin McGuinness over the Enniskillen bombing - but was prevented from doing so by the Northern Ireland Office, it was claimed today.
The astonishing allegation came during a meeting of the Northern Ireland Affairs Committee at Westminster.
Twelve people died when an IRA bomb exploded on Remembrance Sunday in 1987.
Kenny Donaldson, a victims campaigner in the Fermanagh area, said he had been told by a senior investigator with the now-defunct Historical Enquiries Team that investigators wanted to question Mr McGuinness about the atrocity.
Sinn Fein says Martin McGuinness "totally rejects" attempts "based on unsubstantiated hearsay to link him to the Enniskillen bombing"— Adrian Rutherford (@arutherfordNI) September 9, 2015
However, he told MPs that the NIO had advised that it “would not be a good idea”.
Mr Donaldson said he was told nothing more came of the matter.
"We have been advised by a senior former HET investigator that he had cause to wish to bring in the Deputy First Minister for questioning in regards to that atrocity,” Mr Donaldson said.
“He was prevented from doing so. The NIO advised that that would not be a good idea, and it didn’t happen.”
A Sinn Fein spokesman said Mr McGuinness "totally rejects" the claims.
He said: "Martin McGuinness totally rejects this attempt based on unsubstantiated hearsay to link him to the Enniskillen bombing.”
Eleven people were killed and 63 others were injured when the no warning bomb ripped through the Co Fermanagh town on November 8, 1987.
A 12th victim school principal, Ronnie Hill, spent 13 years in a coma and died in 2000.
No one has ever been convicted in connection with the massacre, among the worst of the Troubles.
Stephen Gault, whose father Samuel was killed in the bombing, told the Belfast Telegraph: “It is one step too far that the government can try and sweep this under the carpet.
“Everybody deserves truth and justice.”
In 2013 First Minister Peter Robinson said the PSNI “should be talking” to Mr McGuinness if there was evidence to suggest he knew anything about the Enniskillen bombing.
Mr Robinson told the Impartial Reporter newspaper that he had never spoken to the Deputy First Minister about the attack, but added: “If there is evidence that suggests that he has information then it is the police who should be talking to him, not me.”
Previously Mr McGuinness has said he felt ashamed when incidents such as the Enniskillen bombing were carried out in the name of Irish republicanism.
He made the comments on RTE as part of the Irish State broadcaster’s coverage of the 2011 presidential election.
When asked about the Enniskillen bombing, Mr McGuinness said: “I feel ashamed when incidents like that happened.
“I know that the journalists, if they had the opportunity, would blame me for the 1916 Rising and the war of independence.”
In 2008 a BBC documentary claimed Mr McGuinness knew of the IRA’s plans to bomb Enniskillen.
Journalist Peter Taylor alleged he was the leading figure on the IRA’s Northern Command at the time of the attack.
In the TV documentary ‘Age of Terror: 10 Days of Terror’, Mr Taylor said Northern Command knew about the bombing beforehand but did nothing to prevent it.
Mr Taylor said: “British and Irish security sources on both sides of the border have each independently told me that Martin McGuinness, now Northern Ireland’s Deputy First Minister, was the leading figure on Northern Command at the time of the attack.
“In the hours after the bombing, my sources say that McGuinness travelled to Fermanagh to question members of the local IRA unit to find out what had gone wrong.”
At the time Mr McGuinness said allegations were “completely false” and based on “untrue briefings from faceless individuals in the intelligence apparatus long hostile to Sinn Fein”.
The NIO have been contacted for comment.