Gardaí have begun a murder investigation following the discovery of a man's body in a flat in Dublin at the weekend.

Gary O'Brien, 51, was found dead in a basement flat in a house on Dublin's North Circular Road at around 8.40pm on Sunday after gardaí were called to the scene.

He had been shot in the forehead.

Two people, a man and a woman, have been arrested on suspicion of murder.

The search for the gun intensified today as gardaí continue to try to establish the circumstances surrounding Mr O'Brien's death.

The father and grandfather, who had limited mobility, was originally from Barry Avenue in Finglas but had been living in the flat for the past eight years.

Gardaí believe at least two other people were in the room at the time and left with bloodstained clothes.

Along with the house where the shooting took place and a second one a hundred metres down the road, gardaí today sealed off a third house for a time as the search for the gun continued.

They believe people were moving between the three locations and had been consuming a lot of alcohol and drugs.

A man and a woman in their 30s have been arrested; one late last night, the other in the early hours of this morning.

They are being detained on suspicion of murder and can be questioned for up to a week.

Gardaí today appealed to anyone with information on the incident, particularly in relation to the gun or the disposal of any other evidence, to come forward.