The Police Ombudsman's office has appealed for information about an incident last Sunday in which a man drowned in Carlingford Lough.
The man who died had been swimming off the shore at Warrenpoint.
It is believed the vehicle he had been driving shortly before his death had been stopped by police.
The Ombudsman wants to hear from anyone in Warrenpoint's Rostrevor Road area between 0445 BST and 0600 BST on 15 May who has not yet spoken to them.
The man was named locally as Lewis Murphy, who was in his 40s and from Rostrevor.
Police officers called the Belfast Coastguard to help find him after seeing him go into the water.
A helicopter was scrambled and Kilkeel Coastguard and an inshore lifeboat also joined in the search. A body was recovered a short time later.
The Police Ombudsman's office investigates all incidents in which police officers have been in contact with someone shortly before or at the time of their death.