Saoradh's Ashe Mellon and Melaugh ‘in New IRA leadership'
Two Saoradh activists from Londonderry are also in the leadership of the New IRA in the city, security sources have told BBC Spotlight.
Thomas Ashe Mellon and Fergal Melaugh were both Provisional IRA members in the 1990s, Spotlight understands.
Spotlight wrote to the men for their responses to the allegations, but they have not responded.
The New IRA, a dissident republican group, was responsible for the murder in April of journalist Lyra McKee.
The 29-year-old was shot dead during rioting in the Creggan area of Derry.
Saoradh - "liberation" in Irish - is a political party formed in 2016 and claims it is "entirely separate" from the New IRA, despite a widespread belief that it is the organisation's political wing.
Police have said there is a cross-over in the membership of both organisations.
Last month, a PSNI officer told a court that Saoradh's HQ in Derry was the "mouth and the hub" of the New IRA.
The New IRA, which has been linked with three other murders, is believed to have been formed between 2011 and 2012.
It followed the merger of a number of smaller groups, including the Real IRA, which itself was born out of a split in the mainstream Provisional IRA (PIRA) in October 1997 over Sinn Féin's embrace of the peace process.
What is Saoradh?
Founded in 2016, Saoradh has the support of prisoners from the dissident group referred to as the New IRA in Maghaberry and Portlaoise prisons.
Several high-profile dissidents, including Colin Duffy and Nuala Perry, have also been linked to the party. It is chaired by Brian Kenna.
According to its constitution, Saoradh's objective is to "effect an end to Britain's illegal occupation of the six counties" and establish a 32-county Irish Socialist Republic.
The party has been highly critical of Sinn Féin in the past, with its chairman describing members as "false prophets who have been defeated and consumed by the very system they claim to oppose".
Saoradh, which has offices in Belfast and Londonderry, campaigns for the release of all republican prisoners.
In 1999, a year after the Good Friday Agreement, Mr Ashe Mellon was arrested in connection with the discovery of bomb-making materials in Donegal.
He was admitted to the Provisional IRA wing at Portlaoise Prison. The charges were later dropped.
Police intelligence linked Fergal Melaugh to one of the IRA's most grave atrocities, a so-called human bomb attack, security sources have told Spotlight.
In 1990, Derry civilian Army cook Patsy Gillespie was forced to drive a vehicle containing a bomb towards an army base on the border between Derry and Donegal, while his family were held hostage.
The bomb was detonated by remote control at the entrance to Coshquin barracks, killing Mr Gillespie and five soldiers.
Mr Melaugh was one of six men arrested the next morning, a few miles away in Donegal.
He was charged with IRA membership but was acquitted. He was never charged in connection with the proxy bombing.
Spotlight asked Mr Melaugh about this allegation. He has not responded.
Spotlight understands from several sources that both Mr Ashe Mellon and Mr Melaugh were also in the leadership of Republican Action Against Drugs (RAAD) in Derry in the 2000s.
The self-styled vigilante organisation largely targeted alleged drug dealers.
Neither Mr Mellon nor Mr Melaugh has responded to Spotlight correspondence about this allegation.
RAAD amalgamated with the Real IRA and independent dissident republicans to form the New IRA in 2012.
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