A GARDA cold case review into the murder of teenager Raonaid Murray in 1999 has concluded and the circumstances of her death remain a mystery.

The Sunday Tribune understands the final report by the Serious Crime Review Team – commonly known as the cold case unit – is currently being drafted. The report, which will then be examined by local gardaí in Dun Laoghaire, south Dublin, and garda management, will make a series of recommendations.

Raonaid Murray (17) was stabbed to death while walking to her home in Glenageary, south Dublin, in 1999. Three years ago, the cold case unit, led by Detective Superintendent Christy Mangan, launched a review of one of Ireland's most infamous murders.

The investigation, in conjunction with local gardaí in Dun Laoghaire, initially progressed well. Detectives identified three women, two living in the UK and one in the United States, who were all acquaintances of the teenager and whom gardaí initially considered travelling to interview. However, after further evaluation, gardaí decided against travelling abroad to interview these women about Raonaid's murder.

That decision does not prevent local gardaí in Dun Laoghaire from travelling abroad to interview these women if it is deemed necessary in the future. Like all unsolved murders, Murray's killing remains open but the cold-case unit's involvement in it has now ceased.

In September 2009, it appeared the investigation had a breakthrough of sorts. Gardaí launched a public appeal in an attempt to identify two people seen near the murder scene around the time the 17-year-old was stabbed to death.

Gardaí said the two, a man and a woman, were "people of interest" in the investigation. However, these individuals have still not been located by gardaí.

A number of people were questioned during the initial probe but no one was ever charged. No clear suspect has ever been identified.

The original garda investigation – as well as the cold case review – has been extensive. More than 8,000 original statements were taken and 3,000 people were interviewed. Because of the huge number of statements taken, the review took a long time to complete. In the middle of its review, the unit made a number of recommendations.

Murray's body was found by her older sister, Sarah, on a road close to her home at Silchester Crescent, Glenageary, south Co Dublin, in the early hours of Saturday 4 September 1999. She had been stabbed repeatedly and had bled to death.

Meanwhile, the cold case unit had its first major success last July when a case it reviewed led to a conviction. Vera McGrath (61) was sentenced to life in prison after being found guilty of murdering her husband, Brian McGrath, at their Westmeath home 23 years ago.

Since 1980, there have been 207 unsolved murders in Ireland. The cold case unit was set up to re-evaluate all the evidence objectively in each murder and try to progress the case.

Officially, gardaí have released the names of less than a dozen murder cases they are probing. However, the cold case team is currently involved in reviewing 70 unsolved murders across Ireland.

Various modern investigative techniques such as forensic advances and changes in how evidence is handled mean that cases that have been 'cold' for years can see major progress once the original case is reviewed.