They are issuing an appeal for anyone who witnessed the incident and have not yet come forward.
Shortly after 10:15am last Saturday, Gardaí and emergency services were alerted to the collision, involving a lorry and a pedestrian.
The male pedestrian, aged in his 60s, was pronounced dead at the scene.
Gardaí are appealing to anyone who may have witnessed this collision to contact them.
Any road users, who may have camera footage (including dash-cam) and were traveling in the area of Old Cross Square, Monaghan between 10:00am and 10:30am are asked to make this footage available to investigating Gardaí.
Gardai would also like to speak to a woman who had a child with her walking from the Pound Hill, about the time of the incident.
If you can help, please contact Monaghan Garda Station 047 77200 or the Garda confidential line on 1800 666 111.
