Police have named the 40-year-old who died after being found with head injuries in Crossmaglen as Michael Kirk.
The incident surrounding the Monaghan man's death is now being treated as a "suspected hit and run".
The father-of-two died after being found on the Blaney Road with head injuries following a police report just after 5am on Sunday (Aug 23).
It is understood he was originally from Inniskeen but had been living in Shercock.
Detective Inspector Michael Winters said: "A 35-year-old man presented himself to police last evening and he was subsequently arrested on suspicion of a number of offences. He remains in custody at this time.
"I am keen to trace the last movements of Michael on the night of Saturday, 22 August and the early hours of Sunday, 23 August. Did you see him in the town of Crossmaglen or walking along the Blaney Road?
"I would also like to trace the movements of a blue Audi A6. Did you see this vehicle at any time on Saturday, 22 or Sunday, 23 August, do you have any dashcam footage that could assist us with our enquiries?
"If you have information call us on the non-emergency number 101, and quote reference number 515 of 23/08/2020.
"A report can also be made using the online reporting form via www.psni.police.uk/makeareport."
