A black box recorder installed in the police vehicle involved in the collision which claimed the lives of four police officers could hold vital information about what exactly happened in the early hours of yesterday morning.

Hours after the fatal crash, a senior police officer confirmed the 4x4 Shogun collided with a wall at a bridge on the main Rostrevor to Warrenpoint road before bursting into flames. Four men, named locally as Declan Greene and Kenny Irvine (both from Kilkeel), Kevin Gorman from Drumaness near Ballynahinch and James Magee from south Down, lost their lives.

Unconfirmed reports suggest a motorist — possibly a taxi driver — who was driving along the road behind the police vehicle tried in vain to offer assistance to the officers before the emergency services arrived.

A police spokesman stressed that “the circumstances of the incident are still being established therefore we are unable to provide further details about the collision itself at this time.”

However, he ruled out speculation the men had been trapped in the vehicle by a locking system and said: “We can clarify that the Shogun vehicle involved in this morning's incident does not use self-locking or automatically-locking doors.”

Judith Gillespie, the PSNI’s assistant chief constable for rural region, confirmed the 4x4 caught fire after hitting with the wall and said the crash was a “single-vehicle road traffic collision”, stressing no other car was involved.

She also revealed that a full investigation into the tragedy has been launched and said part of the focus of the probe will be examining the vehicle’s black box.

Ms Gillespie said the four officers who died were responding to a request from colleagues for assistance when the fatal collision occurred.

Paying tribute to the professionalism and commitment of all four men, she also spoke of the shockwaves the deaths have sent around the PSNI and said supporting the families of the officers was “our immediate priority”.

Confirming a senior investigating officer has been appointed in a bid to ascertain what happened, Ms Gillespie said: “The investigation is at a very very early stage but the investigation will take its course.”

She said it was “too early to speculate” whether the wintry weather conditions were a factor in the collision.

The policewoman added: “The vehicle collided with a wall at a small bridge over a river then caught fire.

“At exactly what point it caught fire is not clear.”

Ms Gillespie issued a message of gratitude to staff from Fire and Rescue Service and the Ambulance Service who came to the assistance of the four officers.

She also appealed for anyone who was travelling on the main Rostrevor to Warrenpoint road around 4am yesterday and who may have witnessed the collision to come forward.

Also expressing his shock at the weekend tragedy was Terry Spence, chairman of the Police Federation for Northern Ireland.

Mr Spence revealed that within hours of the horror smash, he received messages of support from the chairman of the Police Federation in England and Wales as well as colleagues in Scotland and the Republic of Ireland.

Saying the events had transcended the “geographical boundaries of Northern Ireland”, Mr Spence spoke of his “deep shock” at the loss of four lives and said “words cannot express how we feel.

“This is something that will live with us for a very long time to come.”