Spanish police who arrested John Gilligan have found a gun that matches the description of the weapon used to kill Veronica Guerin.
The journalist was murdered while stopped at a red light just outside Dublin in 1996.
Spanish police say they have arrested a known Irish criminal after an investigation into a shipment of cannabis and pills to the UK and Ireland.
John Gilligan was taken into custody along with six others in Alicante.
Following the arrest, a search took place around a house where a Colt Python revolver was discovered.
The model found matches the one which was used to kill Veronica Guerin in 1996.
Spanish police say they are liaising with Gardaí to determine if it is the same weapon.
John Gilligan had been tried and acquitted of Veronica Guerin's murder in 2001.
A spokesperson for the Gardaí have said they are working closely with Spanish National Police.