Gardaí have launched a major security operation after convicted murderer and gangland boss Brian Rattigan threatened to murder several gardaí in court last week.

It is understood Rattigan walked up to at least two senior detectives in court last Monday and threatened them. He told one he would "blow the head off him" and told the other he was a "dead man" and made the sign of a gun with his hand.

The trial judge was not informed of the threats which took place shortly before the jury went out to deliberate.

One of the threatened gardaí was also targeted by Rattigan's gang in November 2005 and had a bullet placed on the windscreen of his wife's car at their family home.

Gardaí are taking the threats seriously and say there is little doubt Rattigan has the means to carry out murders. Extra garda patrols have been ordered around the detective's home and there is a possibility he will be offered armed protection.

Rattigan (28), from Cooley Road in Drimnagh, was last week convicted of the murder of Declan Gavin, who was stabbed to death in Crumlin in August 2001. Rattigan is the leader of one of the gangs involved in a feud that has left 16 people dead in eight years.

He has been orchestrating murders from his cell in Portlaoise prison and when gardaí found a mobile phone there four years ago pictures from a murder scene had been sent to him from gang members. They also found a pet budgie named Shrek.

Rattigan organised a campaign of intimidation against witnesses who were lined up to give evidence against him in the trial; several took to the witness box saying they could not remember the events of the night of the murder. One witness was given a two-year jail sentence for contempt of court after refusing to give evidence.

After the guilty verdict was handed down a female associate threatened that Declan Gavin's brother was going to be shot.