A 9.22pm on February 15 North Wales Police received a call that a vehicle had overturned near Yew Tree Farm on the A 548 in Sealand, Flintshire.
There were four occupants in the Black Renault Clio.
One 18 year old male was pronounced dead at the scene and three others were taken to the Countess of Chester Hospital.
All three males remain in hospital, one with serious injuries.
Anyone with information is asked to contact North Wales Police on 101, or 0845 607 1001 (Welsh line) 0845 607 1002 (English line) or Crimestoppers anonymously on 0800 555 111.
There are no further details at this time.
