The policeman who witnessed the callous murder of detective Adrian Donohoe has vowed to catch his killers.

Detective Joe Ryan made the vow during a meeting with Ireland’s justice minister Alan Shatter.

The Fine Gael leader met Ryan when he visited Dundalk police station on Monday where the late Donohoe was based.

Ryan told the Minister, ‘I’ll help catch his killers,’ as police on both sides of the border chase the gang who shot Donohue during a raid on a credit union last Friday night.

Ryan was warned that his head would be ‘blown off’ during the robbery as Donohue was shot at point-blank range with a shotgun.

A colleague of Ryan told the Irish Sun: “Joe is a very experienced officer and has been left distraught by his partner’s brutal murder.

“The fact he returned to work so quickly on Monday highlights the true character of the man.

“He’s already spoken with senior investigators from the National Bureau of Criminal Investigation and he is doing all he can to help.

“Joe appreciates the support from everyone in the community and told the Justice Minister of his desire to help the investigation team.

“Just like Adrian, he’s a dedicated and committed to serving his community.”

Shatter paid tribute to Detective Ryan when he spoke to the media after his visit to Dundalk.

The Justice Minister said: “I had the opportunity to meet Joe Ryan and I expressed my good wishes to him.

“We have to admire his courage. He is obviously still upset.

“Everyone in the station is understandably upset. But they are very focused at bringing to justice those who are responsible for the barbaric murder.”

A team of 100 officers are now working on the Donohue murder case.

They believe their colleague was killed by a criminal gang based in North Louth and South Armagh.