The officer is now confined to his station and his family are subject to regular armed garda protection because of the threat, which is regarded as very serious.

The garda was wrongly blamed for supplying the intelligence that Colm Griffin, Eric Hopkins and Gavin Farrelly were planning to carry out a raid on Lusk post office in north Dublin.

Griffin (33) and Hopkins (24) were shot dead by a member of the Emergency Response Unit (ERU) during the robbery when they refused requests to drop their weapons.

Following the two fatal shootings, officers were not certain of the identity of the dead men.

It was known that they were from the north inner city and a senior detective from the area arrived at the scene and confirmed that Griffin and Hopkins had been killed.

Gavin Farrelly had been arrested and saw the detective identify the bodies of his two friends. He knew the garda because he had been involved in a number of prosecutions against him.

Several days after the incident Christy Griffin, brother of Colm Griffin and a well-known serious criminal, called a meeting of at least eight of his associates in the North Star Hotel in Dublin city.

Griffin vowed that he would have the garda who fired the fatal shots assassinated and offered around 50,000 to anybody who would carry out the murder.

However, because the identities of ERU members are closely guarded, the criminals could not find out the name of the officer who had fired his weapon.

Some weeks after the shooting, Gavin Farrelly informed Christy Griffin that he had seen the senior detective at Lusk post office and speculated that he could have provided the intelligence that the raid was planned.

Christy Griffin also knew the detective because the garda had spent the previous few years investigating his criminal activities.

Griffin then decided to place a 40,000 contract on this garda's life and it remains in place today. The information about the Lusk robbery did not come from the detective, but originated from another source.

The highly respected officer was placed on extended leave and is now confined to working in his city-centre station. The threat against him is real and necessitates him checking his car for explosives every time he uses it.

The man's family and house are subject to regular armed patrols and garda squad cars check on the house every half hour. He has even been followed home from work and sources say there is no doubt that Griffin's associates know where he lives.

Christy Griffin (37) was jailed for life earlier this year for the repeated rape and sexual abuse of his partner's 14-year-old daughter. He also blames the detective for this conviction and is said to be obsessed with getting revenge.

There were emotional scenes at the inquest of Colm Griffin and Eric Hopkins last week as the CCTV footage of the fatal shootings was played for the jury.

The footage of the incident was short and very powerful. At 34 seconds past 8.07am on 26 May 2005, two gardai dressed as builders entered the public area of the post office at the back of the Village Store mini-supermarket in Lusk.

Both wore fluorescent jackets and hard hats and approached the screen at the post office, which was closed. The gardai are referred to as Detective Garda A and Detective Garda B at the inquest because their identities are not being revealed.

They were expecting the raiders to enter through the front door but were told on their radios that the raiders' car had driven around to the back of the post office.

Garda A produced his official ID and slid it though the security hatch to show postmistress Linda Neary.

At 49 seconds after 8.07am, Ms Neary opened the locked door into the private offices of the post office and the two gardai went into the back area where there were eight An Post employees unaware that an incident was occurring.

Seven seconds later, the fixed CCTV camera captured three men wearing balaclavas coming towards the post office through the front door of the supermarket, not the back of the post office where the gardai were stationed.

One man had a sledgehammer and began to repeatedly strike the reinforced glass of the security hatch, shattering it.

In the private area of the post office, Detective Gardai A and B heard the commotion and rushed to see what was happening.

Garda A gave evidence that he heard a loud bang and saw the glass in the security hatch shatter. He believed that the loud noise was a gunshot and shouted "armed garda, drop your gun" as he opened the door leading into the public area of the post office.

At least half-a-dozen witnesses gave evidence indicating they clearly heard the officer warn the raiders to drop their weapons. Some witnesses said the garda gave the warning several times;

one man said he warned them on up to 10 occasions.

The CCTV footage showed that at 13 seconds past 8.08am Colm Griffin turned and saw garda A. He held a gun in both his hands in a firing position and aimed it at Garda A.

Just one second later, he slumped to the ground.

Garda A fired two shots. The first struck Griffin on the left side of the body, just under his breast, but did not kill him.

The second bullet went through the back of Griffin's head at the left ear as he began to fall from the effects of the first shot. He died instantly.

Garda A said he fired the second shot because Griffin's weapon was still pointing at him after the first bullet struck.

Eric Hopkins was captured on camera leaning over Griffin's body and, at 15 seconds after 8.08am, he began to move across the public area of the post office towards the main shop.

He had his left arm raised at chest level. Less than one second later he began to stumble.

Garda A had fired one shot which entered Hopkin's heart. He died within seconds.

The officer, giving evidence from behind a protective screen, said he shot Griffin because "there was no doubt in my mind that he was a man prepared to kill".

He explained he fired at Hopkins because he "believed he had taken possession of the gun" when he leaned over Griffin's body. Hopkins did not have a gun when he was shot.

The shooting was over in little over two seconds, and the two men had been in the shop less than 20 seconds when they were killed. Relatives of the dead men wept as the footage was played.

Gavin Farrelly was the man who carried the sledgehammer and was furiously attempting to break the glass at the security hatch. He continued to hit the glass for two seconds after Griffin was shot.

He said he thought Griffin was firing warning shots and maintains that the garda gave no warning, which is in direct contrast to the evidence of several independent witnesses.

Farrelly (35) surrendered when he saw the armed gardai. He pleaded guilty to his role in the incident and is currently serving a 10-year sentence.

The inquest continues next week, when Garda B will take to the stand. Security at the inquest is tight. Every member of the public must go through x-ray machines and are searched for weapons. There are even garda marksmen on the roof for fear that the gardai giving evidence could be targeted.