Four PSNI officers died in an "intense" blaze after becoming trapped when their vehicle crashed on a 999 callout.
Kenny Irvine, Declan Greene, Kevin Gorman and James Magee were killed in the accident near Rostrevor.
The men were aged in their 20s and 30s and were all living in the south Down area.
All four were based at Kilkeel PSNI station.
They were responding to an emergency call when their Mitsubishi Shogun hit a wall and burst into flames during the early hours of November 23, 2008.
The opening day of an inquest into the crash heard pathologists recorded the cause of the men's deaths as smoke inhalation and burns.
Outlining the brief facts of the case, counsel for the Coroners Service Ronan Daly said no other vehicle was involved.
"After the crash these four officers could not get out and others outside attempting to assist could not make their way inside," he said.
"That was due to intense fire flames, smoke, damage to the police vehicle and a blocked escape route in the vehicle."
Mr Daly said the officers were on a "blue light run" after receiving an emergency call about a public order situation in Rostrevor.
The vehicle was being driven by Mr Magee, a 27-year-old constable from Newcastle.
It was travelling from Warrenpoint when it crashed on the Moygannon Road just shortly before 4am.
The crash was the single biggest loss of life since the PSNI's formation in 2001.
The case is being heard before a jury of six women and five men and is expected to last until next Friday.
Relatives of the four men were present for yesterday's brief opening remarks. Mr Daly told the jury that they would hear from a range of expert witnesses and civilians who came upon the scene.
He said there were no witnesses to the crash itself.
Senior members of the PSNI, including Assistant Chief Constable Alan Todd, are expected to give evidence.
The jury will also be shown DVD and video recordings from the scene.
Constables Green (39) and Irvine (30), who were both from Kilkeel, worked as part-time police officers.
Their widows Roisin Green and Andrea Irvine spoke briefly during the hearing to confirm personal details.
Mr Gorman (24), from Ballynahinch, and Mr Magee were employed full-time. Jacqueline Gorman, the mother of Mr Gorman, and Mr Magee's father Bawn also took to the witness stand for a short time before the inquest was adjourned.
It will resume again this morning.