One of the two main suspects for the murder of Detective Garda Adrian Donohoe is now working in the IRA's illegal fuel trade and is regularly seen driving trucks across the border, the Sunday independent can reveal.

The man, who is in his mid-twenties, is believed to have been standing alongside the gunman who fired the single shotgun blast that instantly killed the 42-year-old detective as he guarded a cash delivery from Lordship Credit Union two years ago today.

The suspect is regularly driving trucks across the Border delivering the illegal diesel that is the IRA's main source of criminal finance.

He is not a member of the IRA, but works for a relative who gardai described last week as the 'number two Provo' under the IRA boss who controls the fuel laundering trade in south Armagh.

Garda believe that the suspect's connection with the south Armagh IRA gangsters is one of the main reasons the gang that murdered the detective and father-of-two is being shielded by the unwritten code of silence similar to that of the Mafia's 'Omerta'.The murder suspect was identified along with four other members of the gang within days of the killing on January 25, 2013 - yet all remain free.

Garda sources said that there are several witnesses that could provide evidence but no one has come forward.

The main suspect for firing the fatal shot is also back living in south Armagh and is suspected of being re-involved in criminal activity.

Garda sources said he is "up and down the road" - meaning that he is crossing the Border into the Republic on a regular basis.

Two other members of the gang, brothers from south Co Down, who are also involved through relations with the fuel smuggling trade, left Ireland and are now illegally resident in the United States.

Garda detectives attempted to question them in New York a year ago, but they declined to present themselves for questioning.

Before the murder of Adrian Donohoe these brothers were involved in a dispute with other major IRA fuel smugglers and an attempt was made to 'kneecap' both.

It was partly as a result of this dispute, according to garda sources, that these two have chosen to stay out of the country, rather than fear of being arrested over the murder of Det Gda Donohoe.

The fifth member of the gang, from Crossmaglen in Co Armagh, also left Ireland in the aftermath of the detective's murder for the United States, but he returned last year.

This suspect also remains living in south Armagh.

Garda sources insist the investigation has made "significant" advances in terms of locating movements of the gang members on the night of the murder but this is not sufficient to establish charges.

The gang burnt out the stolen Volkswagen Passatt car they used in the robbery and there is no DNA or other forensic evidence. The car was left burnt out near Darkley in south Armagh.

At the time, the gang was based near Cullyhanna in south Armagh and travelled through back roads to this location before dispersing.

Senior gardai say they are still pursuing some 4,200 'lines of inquiry'.

However, sources say the investigation has progressed relatively little since the early days when the gang disappeared into the protection of relatives and associates in south Armagh.

One of the 'active' lines of inquiry is the monitoring of social media as all members of the gang were active on Facebook.

Around 600 people, led by his widow, Caroline, attended a vigil for Det Gda Donohoe in Dundalk on Friday night. Mrs Donohoe and her two children carried flowers ahead of the mourners in a brief walk from Lordship Credit Union to the nearby St Patrick's GAA club where he trained junior teams.

Garda Commissioner Noirin O'Sullivan is due to attend mass in St Joseph's Redemptorist Church in Dundalk this morning to mark the second anniversary of the murder.

Sunday Independent