It comes after a cyclist, aged in his 80s, was discovered unresponsive on a road in Batterstown, Ballivor last Friday.
He was taken to Connolly Hospital in Blanchardstown where he was pronounced dead.
On Wednesday, gardai arrested a man in his 40s.
He can be detained for up to 24 hours.
A vehicle has also been recovered by gardai.
Investigating gardai at Trim Garda Station continue to appeal to the public for information.