Crimestoppers has launched an appeal for information in relation to the murder of Andrew Allen in 2012.
He was killed in Buncrana, Co Donegal on Thursday February 9th of that year.
Mr Allen moved to Buncrana after he became the target of the vigilante group 'Republican Action Against Drugs' in his native Derry City.
Detective Inspector Pat O'Donnell said: "This activity persisted and three years ago in February 2012 he was murdered by a group of individuals in Buncrana."
"We believe that there were a large number of individuals involved on the night of Andrew's murder. However, our understanding is that some of these individuals did not intend for the events that unfolded to lead to his death."
They are appealing to these individuals, or any others involved on the night, to come forward.
They can anonymously contact the Crimestoppers line on 1800-25-00-25, or the gardaí.
The appeal is being jointly run with Crimestoppers Northern Ireland. Calls to Crimestoppers NI can be made from within Northern Ireland on freephone 0800-555-111.
