British security forces did not share key information with An Garda Síochána that could have aided an inquiry into the 1972 Belturbet bombing that killed two teenagers, RTÉ Investigates has learned.

While nobody has ever been convicted for the 28 December bombing that killed Geraldine O'Reilly, 15, and Paddy Stanley, 16, confidential British Ministry of Defence files reveal that, from just four months after the incident, security forces in Northern Ireland were aware of a "Commando type gang" who they believed were responsible for "various explosions" south of the border.

Records released by the Ministry of Defence to the UK National Archives and obtained by RTÉ Investigates also identify the leader of the gang as Billy McMurray, a member of the Ulster Defence Association from the loyalist enclave of Rathcoole outside Belfast.

None of this information was shared with gardaí.

Mr McMurray subsequently served six months in jail for unrelated firearms charges and was also linked by the Royal Ulster Constabulary to the December 1972 murder of Louis Leonard in Derrylin, Co Fermanagh.

A summary review compiled by the PSNI's Historical Enquiries Team, which, between 2005 and 2014, re-examined unsolved murders committed during the Troubles, confirmed that "in late 1972 intelligence was received" that Mr McMurray, described as "Suspect A", was the organiser behind "a UDA team ... formed to carry out terrorist attacks in the south and north". The same review described McMurray as "acting lieutenant colonel for Fermanagh and Tyrone".

Read the full investigation:
The Belturbet bomb: an atrocity that time forgot

The PSNI declined to explain to RTÉ Investigates why none of this information was shared with gardaí.

Relatives of the victims are likely to ask the same question, particularly as it appears that this intelligence was received by the RUC before the 28 December attack.

In a statement, the PSNI said it would "provide cooperation and assistance as required by any current or future investigation by An Garda Síochána".

In response to a series of questions relating to what the gardaí knew about Mr McMurray, the Garda Press Office told RTÉ Investigates that it does not comment on ongoing investigations.

The Ministry of Defence in London also declined to comment on the matter.

In the 48 years since the Belturbet attack, An Garda Síochána have compiled six separate reports on the incident. The details have not been released publicly nor disclosed to the families of the teenagers killed. 

Gardaí contend that divulging information to relatives could "interfere with the investigation ... [and] could reasonably be expected to affect adversely the security of the State, matters relating to Northern Ireland and the international relations of the State".

The confidential British military and PSNI files were obtained by RTÉ Investigates during a seven-month-long investigation into the circumstances surrounding the Belturbet bombing.

Watch the RTÉ Investigates documentary Belturbet: A Bomb That Time Forgot tonight at 9.35pm on RTÉ One and RTÉ Player.