The Garda Ombudsman Commission is investigating the circumstances surrounding a crash in Co Mayo last night.
Two men, a 19-year-old man and a garda in his 40s, were killed in the crash, which occurred around 1km outside Belmullet.
They have been named as Stephen Conway and Garda Terence Dever.
A third car, being driven by another off duty member of the force, was also involved in the incident.
Three off duty gardaí were travelling to work in two vehicles, when a motorist approached in the opposite direction.
The Garda in the first car swerved to avoid the car, but the oncoming vehicle crashed head on into the car carrying two other members of the force.
Mr Conway from Barr na Tra was killed instantly.
The two gardaí were injured and transferred to Mayo General Hospital in Castlebar, where one died a short time later.
His colleague is said to be in a serious condition in hospital, but his injuries are not believed to be life threatening.
Gardaí say driving conditions were good at the time of the crash.
In a statement, Garda Commissioner Fachtna Murphy said the tragedy added to an increasing number of fatalities on Irish roads in recent weeks and he urged all motorists to take extra care when driving.