A probe into the murder of a hero garda was cracked as US cops gathered critical information about the on-the-run gunman.

The Irish Mirror has learned officers hunting the killers of Detective Garda Adrian Donohoe were in constant contact with American authorities.

This included the Homeland Security Investigations (HSI), who were monitoring the chief suspect in New York.

A US source said:“The suspect was in pubs and in the general Irish community – he thought he was safe but he wasn’t.

“There were some good people in this community who sent information back home. This was then used by the Irish investigators who sent it to the HSI.

“High level cross-Atlantic operations were launched then and good information of an evidential nature was gathered.”

The suspect was sent home on foot of an extradition order for minor offences.

On his arrival in Ireland he was imprisoned for the unrelated offences. At present two men are detained by gardai under anti-gang legislation.

The men, one in his 20s and the other in his 60s, can be held for up to seven days.

One was arrested last Sunday night and the second late on Monday night.

Last week the Irish Mirror revealed Boston-based HSI agents are hunting for information about the two brothers from the North who are on the run in the city.

Posters were placed in the strong Irish emigrant areas of Dorchester and Quincy communities.

An offer of a reward was made and numbers for the HSI, gardai and other law enforcement agencies.