Four people have died in three separate road crashes within a 36-hour period.
Pedestrian Sean Reid, 69, was struck by a car on the Great Northern Road in Omagh at about 11:20 BST.
The police said one person was assisting with their enquiries.
Tonight I am deeply saddened to learn that a 3rd life has been lost on the A5 rd since yesterday.— Daniel McCrossan MLA 🕊 (@McCrossanMLA) September 4, 2018
A 69 year old man sadly lost his life after a collision this morning.
My deepest prayers are with the families of all involved in what has been a tragic loss of human life.
Meanwhile, a married couple in their 70s, died in a separate collision in County Tyrone on Monday afternoon. They were killed when a car and a lorry crashed on the Doogary Road in Omagh.
The lorry driver was uninjured.
PSNI Insp Keir Kitt said: "I am appealing for witnesses or anyone who was travelling on the Doogary Road between 2:30pm and the time the collision was reported to us to contact us.
"I am especially keen to hear from anyone who may have captured dashcam footage of the collision, or believe they saw the Volvo car prior to the collision."
Meanwhile, a woman from County Tyrone, named locally as Joanne Tracey, died following a two-car collision near Drogheda in County Louth.
The crash happened between junctions 10 and 11 on the M1 northbound at approximately 01:20 BST on Monday.
It is understood Ms Tracey was returning home after attending the GAA All-Ireland final between Tyrone and Dublin in Croke Park.
The driver of the other car was uninjured.
SDLP West Tyrone MLA Daniel McCrossan said: "My heartfelt sympathies go out to their family and loved ones. The times ahead will be difficult for them but I know the local community will rally round and do all they can to help and support them."
Gardaí have appealed for witnesses to contact officers.