Two pedestrians were killed when they were hit by a police car responding to an incident in Bedfordshire.
The men died when the car came off the road after colliding with another vehicle in Luton at 2351 BST on Friday.
The victims, believed to be Algerian nationals in their 20s and 30s, were on the path at the junction of Holland Road and Leagrave Road.
The force has referred the incident to the Independent Police Complaints Commission (IPCC).
The junction was closed while the investigation was carried out.
A Bedfordshire police spokeswoman said: "The marked panda car, crewed by two male police officers from Luton, was responding to an immediate call for assistance and was on blue lights and a siren when it first collided with a Toyota Celica being driven by a man who was alone in the car."
Neither of the two police officers who were in the car nor the driver of the other vehicle were injured.
The IPCC said it had sent investigators to the scene of the collision.
IPCC deputy chair Deborah Glass said: "My thoughts are with the families of those who died as a result of this tragic incident.
"We will be conducting a rigorous investigation into the circumstances surrounding the collision - including whether or not the police car's lights and sirens were activated - and our investigators continue to secure evidence in relation to the incident."
The IPCC said efforts to contact the victims' next of kin were continuing. The two men were on their way home from work at the time of the crash.