Private Barrett, from Letterkenny, Co Donegal, died from a single gunshot wound to the head while serving with the Unifil mission in south Lebanon, while two colleagues were in his sleeping quarters.

He was found dead in the sleeping quarters of an observation post at the 84th Infantry Battalion Unifil base in Bra'Shit on 17 February 1999.

The 21-year-old's own service rifle lay beside his body.

The internal military police investigation noted that the shooting "was accidental and that no physical evidence was found to suggest that Barrett had any intention of committing suicide". Unifil investigators concluded it was a tragic accident and nobody else was sought in relation to his death.

However, the military inquiry into the killing was sharply criticised. It did not amount to "an effective investigation, " senior counsel Seán D Hurley said in a report to defence minister Willie O'Dea.

Following Hurley's 2005 report, the minister referred all files on the case to the gardaí.

Hurley's inquiry was sparked by pressure from the dead man's family. His mother, Helen Barrett, told the Sunday Tribune in a 2004 interview that she had received information from several of her son's army colleagues indicating that his death was linked to a dispute with another member of the Unifil Battalion on duty in Lebanon.