The FBI has intensified its investigation into two men suspected of involvement in the murder of Det Gda Adrian Donohoe and who fled to the US after his death.

It comes as the suspected gunman in the callous killing is expected to walk free from prison in the coming days.

The two suspects in the US, who are brothers, have been living among the Irish communities in Boston since their involvement in the heroic garda's murder in 2013.

Gardaí have been liaising with several international police agencies, including the PSNI and the FBI, as part of the investigation.

Federal agents in Boston and the local police have increased pressure on two of the five-man gang living in the area and have offered a substantial reward for anyone who can give information to assist them.

Posters distributed by the FBI in recent weeks in north Boston state: "Investigators believe people living in Boston and the upper Norfolk County towns of Massachusetts may have information that can assist the investigation.

"A substantial reward is being offered for any information leading to the arrest and convictions of the person(s) involved."

The FBI and US police have specifically appealed for information from the area's Irish community.

Senior gardaí previously vowed they will go "to the ends of the earth" to bring Det Gda Donohoe's killers to justice.

In the coming days the criminal suspected of being the gunman in his murder will be released from a Dublin prison after being jailed for motoring offences.

The man, aged in his 20s, was extradited from the US last year after hiding out in New York and Boston following the murder. The other two criminals involved in the murder are currently living freely in the North, despite the investigation involving the PSNI.

Det Gda Donohoe, a father-of-two, was murdered during an armed robbery at the Lordship Credit Union near Dundalk, Co Louth, on January 25, 2013.

On the fifth anniversary of the murder last month, senior gardaí said the killers were being shielded by family and friends.

Chief Supt Christopher Mangan said those providing support to Det Gda Donohoe's killers "will never have peace" until they come forward with information about the murder.

"The persons involved in this murder have no doubt received logistical and emotional support from their families and friends," he added.

Irish Independent