Memorial services will take place later to mark the 30th anniversary of the killing of eight men and women in the Co Londonderry village of Greysteel.
Eight civilians, both Catholics and Protestants, died following the attack at the Rising Sun bar on October 30, 1993.
Seven were killed on the night of the attack, while the eighth died several months later from injuries.
UDA/UFF gunmen shouted “trick or treat” before pulling the trigger.
I hope we can remember the past with a graciousness and forgiveness— Catholic Bishop of Derry Donal McKeown
Secretary of State Chris Heaton-Harris said on the 30th anniversary of the atrocity his thoughts are “very much with all those impacted by the horrific events of that day”.
Alliance Party leader Naomi Long said it was “one of the most horrific periods of the Troubles”, and paid tribute to those bereaved at Greysteel as remaining “strong and dignified”.
Karen Thompson, 19, Steven Mullan, 20, Moira Duddy, 59, Joseph McDermott, 60, James Moore, 81, John Moyne, 50, John Burns, 54 and Victor Montgomery, 76, are set to be remembered during a special Mass at the Star of the Sea church.
Later, a cross community prayer service will take place at the memorial to the shooting in Greysteel village.
The atrocity came just days after a Provisional IRA bomb killed nine people at a fish shop on the Shankill Road in Belfast, and was regarded as a retaliatory attack by loyalists.
One of the IRA bombers was also killed in the blast.
Catholic Bishop of Derry Donal McKeown said the commemorations at Greysteel will be “tinged with sadness and tears but etched with hope”.
“Remembering is important, but I think we want to ensure that we don’t spend all our time being being stuck in the past,” he told the BBC.
“It’s how we remember makes all the difference, and I know this community, and so many communities all round Northern Ireland, have found ways of remembering the past with compassion, not in any way denying the terrible things that happened, the awful effects of hatred, and I hope that we can remember these people who died with love.
“I hope we can remember the past with a graciousness and forgiveness.”
Church of Ireland Bishop of Derry and Raphoe Andrew Forster said he believes the horror of that week created a momentum for change.
“It was a time whenever we thought this couldn’t get any worse,” he said.
“There was a massive sense of fear, there was a huge sense of despair and in some way there came a movement out of that week where people said ‘this can’t go on’.
“People had been living with the reality of violence that was going on, but for scale of it and the absolute hatred and horror of that week, I think it made normal people think ‘this can’t go on’, and there was a momentum in the change that needed to happen.
“It’s hugely important that we remember them (weeks like that) because we remember those who are left behind and our hearts go out to them, but we also remember that we can never go back to that.”
Kenny Donaldson, director of the victims group South East Fermanagh Foundation (SEFF), said the murders sent shockwaves near and far.
“Those who committed that atrocity will claim that it was revenge for the Shankill attack one week earlier. The truth is that the murders were motivated by sectarian hatred,” he said.
“SEFF representatives will be present on Monday night to show solidarity with all those impacted. Greysteel was wrong and without justification, just as the Shankill bomb was and all other innocents who perished over that horrific week in our history but also those others murdered before Shankill and after Greysteel.”
