Police are looking for two men that left the scene where a 27-year-old officer died in a road crash involving a suspected stolen vehicle.
The officer was travelling in a police car on routine patrol when the incident happened in Londonderry last night.
Two other officers in the patrol car sustained non-serious injuries.
Police have appealed for witnesses to come forward.
More top news
Madonna says she still cannot bring herself to watch footage of the moment she fell on stage while performing at the Brit Awards.
Ed Miliband has pledged to give zero-hours workers the right to convert their contract into a regular job after three months.
More than 100 leaders have declared their support for a Conservative-led government, warning a Labour would "put the recovery at risk".