“The Darkley massacre stands as one of the most horrific atrocities of the Troubles.”
On November 20 1983, three gunmen attacked worshippers at a Sunday evening service. Church members Harold Brown, Victor Cunningham and David Wilson were killed. Seven others were injured.
No-one has been convicted over the attack.
Mr Irwin described the attack as “indiscriminate sectarian murder”, adding the victims were targeted, “because of their faith and were easy targets in the small isolated wooden building”.
He continued: “Even amongst the horrors of the Troubles, Darkley stands as one of the most horrific atrocities as gunmen stood outside the church, reloading their weapons to then spray the building with gunfire again.
“Mountain Lodge has seen the murder of its members and arson attacks on its premises on two separate occasions. Despite Sinn Fein’s view, there was never any justification for such attacks and there was always an “alternative” to such hatred.
“Even after 40 years it is difficult to comprehend the mindset of those who perpetrated this atrocity. It is also hard to find a more glaring contrast than between those who were inside the building that evening and the gunmen who attacked them indiscriminately.
“It is also difficult to comprehend how, even after four decades there are still those in our society who eulogise and celebrate the types of individuals who were involved in preparing and perpetrating this massacre.”
David Robinson, a parishioner at the time, said the three men who died happened to be at the front door.
Recalling the incident on the 30th anniversary for the BBC, Mr Robinson, said: “They were there to kill anyone. The three men that got killed just happened to be at the front door. They didn’t finish with that. They went outside and up the outside of the building with a machine gun… basically trying to kill everybody inside.”