They're asking one motorist in particular to come forward.
Gardaí are appealing for witnesses to a serious assault in Offaly.
A man in his 30s was sustained head injuries in the attack on Francis Street, Edenderry yesterday evening.
Another man in his 20s was arrested and is being questioned at Tullamore Garda Station.
Gardaí are particularly appealing for the driver of a dark blue people carrier, with a roof rack, to come forward.
The car was forced to stop on Francis Street at 6.05 yesterday evening, when the two men moved onto the road.
Witnesses are asked to contact gardaí at Tullamore Garda Station 057 932 7600 or the Garda Confidential Line 1800 666 111.