Detective Joe Ryan, the partner of murdered cop Adrian Donohue, was warned that he would be shot in the head if he came to the aid of his dying friend.

Ryan and Donohue were on escort duty for a large consignment of money leaving the Lordship Credit Union at Bellurgan, near Dundalk in Co. Louth  after closing on Friday night.

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The detectives noticed a suspicious looking dark-colored car in the credit union parking lot with three men inside it. A fourth man was waiting by the car as if on a lookout. As Det Donohue began to get out of the car to investigate when one of the men opened fire and shot him in the head with a shotgun.

‘Detective Ryan was told he too would be shot if he took another step. The gang then took the keys of the garda car before taking off,' a source told the Daily Mail.

‘They clearly panicked once they saw Adrian get out of the car but they were cool enough to take their keys.

‘And this was all for the sake of small money. It’s beyond belief.

‘They didn’t even give him a chance. No words were exchanged and he did not have his weapon in sight. He was shot before he even got a chance to stand up as he got out of the car.

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‘He fell to the ground and died instantly. It’s absolutely appalling. The whole community is devastated – he was a very popular family man.’

The men, who are believed to have been carrying a handgun as well as the shotgun, then drove away out of the village as Det Ryan rushed to call for backup. A massive manhunt is now under way to track down the killers.

Police have said they were doing ‘everything in their power’ to bring the perpetrators to justice.  All the major national units including the Bureau of Criminal Investigation, the Special Detective Unit and Air Support Unit are involved in the hunt.

‘This is a cold-blooded murder,’ said Superintendent David Taylor. ‘Detective Donohoe had just alighted from the car. The scene was chaotic and we don’t have the exact timeline. He just stepped out of the car and was fatally wounded.

‘Detective Ryan is absolutely traumatised. It was a traumatic event for him to witness. His life was under threat too.’

He said Mrs Donohoe was ‘shattered’ over her husband’s death.

‘She is in bits,’ said Supt Taylor. ‘They have a very young family and they are absolutely in bits.

‘We are particularly interested in a dark coloured car that was seen driving in an erratic manner leaving the scene.

‘We have no indication which direction it went, north or south, and do not have registration details.

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He added: ‘Dr Khalid Jabber attended the scene and later last night the remains of Detective Donohoe were removed to Our Lady of Lourdes Hospital in Drogheda where a full post mortem was carried out today.’

Garda Commissioner Martin Callinan said: ‘I want to assure the family that we will be doing everything in our power to bring the perpetrators of this terrible murder to justice.

‘It is a very, very sad day for An Garda Siochána and for Ireland. We were deeply shocked and saddened by the murder of our colleague while he was carrying out his duty.

‘I just want to say at this time is that my thoughts, and the thoughts of everyone in An Garda Siochána and I am sure the wider community are with the Donohoe family and their immediate and extended families, particularly with Caroline and their two young children.

‘I was in contact last night with the family through my colleagues. Obviously, there is great upset and sensitivity involved so we have to allow them some time.

‘I have received overwhelming support from the Government, from my minister, from the President and many, many more political and community leaders and we deeply appreciate that.

‘This is a cry for help for An Garda Siochána,’ he said.

‘There are people out there who are aware of who these people are and I appeal to those people to come forward and help us. Society needs to make some choices here. We do need the public’s help and this is an opportunity for them to come forward.

‘Up to four people involved in the actual raid and how many were involved beyond that will remain to be seen.

‘We will put all our energy into finding out who precisely was behind this robbery.

‘It is too early to speculate if there is a subversive element in relation to this or if they are criminals, ordinary criminals.’

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It has been 17 years since a policeman was shot dead in Ireland. In 1996, Jerry McCabe was shot in the head as he escorted an An Post van in Adare, Co. Limerick.