Gardai say people in Northern Ireland may hold key information into the 2008 murder of Andrew Burns.
The 27 year old was shot twice in the back at a church car park in Castlefin, Co.Donegal.
It's understood up to three people were involved and one man has already been jailed.
Detectives are continuing a cross border investigation as some of those involved may have traveled to Co.Tryone.
It's understood Mr.Burns was driven to the scene by appointment from his home in Strabane.
Dissident republicans were blamed for the attack at the time.
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