The 41-year-old was shot dead by armed robbers while he was escorting a cash delivery van at Lordship Credit Union, near Dundalk, on 25 January last year.
Detective Donohoe was the first Garda to be killed in 17 years.
An investigating team, working closely with PSNI, have carried out over 2,300 lines of enquiry and interviewed more than 800 people.
Searches have been carried out on both sides of the border and initial CCTV reviewing has been completed, with further detailed examination to follow.
Gardaí said they are making progress in a number of different areas.
Assistant Commissioner Kieran Kenny said at least five people were involved in the incident.
"One person fired the fatal shot that killed Adrian Donohoe," he explained.
"There are people out there who have knowledge of Adrian's murder and I would ask them to reflect on the impact that Adrian's death has had on the family, the Garda Síochána and the community where he lived and where he served. I would appeal to anybody who has information about the murder to contact us please".
Most importantly, his senseless, cold-blooded murder led to the bereavement of Caroline and their two children.
Garda Commissioner Martin Callinan
Garda Commissioner Martin Callinan spoke at Dundalk Station on Friday, the eve of Detective Donohoe's first anniversary.
"It is almost a year since the callous murder of our colleague Detective Garda Adrian Donohoe, who was shot dead while carrying out his normal day-to-day duties as a member of An Garda Síochána," he said.
"His murder had a profound impact not only on his colleagues in Dundalk, but also on the wider An Garda Síochána family.
"It had an impact not only on the lives of those he positively affected in Co Louth through his work, or through his involvement with the GAA community, but also country wide."
Commissioner Callinan added: "It is Caroline and the two children who are uppermost in my mind at this time, as we remember a man who involved himself wholly in his family, his community, and in his job, and who ultimately gave his life in the service of them."
Highlighting the extensive operations so far, he thanked Interpol, Europol, the Dutch Police, FBI and especially the PSNI for their support.
Speaking about PSNI involvement, he said: "The level of support and unstinting dedication shown by them in the course of this investigation is indicative of the close working relationship between the two organisations."
He pledged continuing resources to be made available for the investigation, "for I firmly believe that Adrian's memory is best honoured by seeing those involved in this terrible crime being held accountable for their brutal actions".
Superintendent Gerry Curley appealed for any information on a blue automatic Volkswagon Passat, 08D registration, which was taken during a burglary in the Clogherhead area of Co Louth between 11.30pm on Tuesday 22 and 4.30am on Wednesday 23 January.
It was burnt out at around 10.30pm at Cumsons Road, Newtownhamilton in Armagh on the night of the murder.
Gardaí would also like to identify the whereabouts of a Cosatto car seat that was in the vehicle when it was taken but was missing when the car was burnt out.
Finally anyone who has any knowledge about the origin of a precision mallet type hammer found at the murder scene, which would be used by panel beaters of motor cycle mechanics etc, are also asked to come forward.
Anyone with information can phone in confidence the incident room in Dundalk Garda Station at 00353 42 93 88470.