PHILIP CAIRNS

On 23 October 1986, 13-year-old Philip Cairns left his home at Ballyroan Road, Rathfarnham, to go back to school after lunch. He never made it. In the 20 years since Philip's disappearance his abductor, and probable murderer, has never been caught, despite massive resources being ploughed into the investigation.

Rumour and whispers have always dogged the case, with speculation that Philip was kidnapped by a religious cult or a group of paedophiles who had been abusing him. The fact is that nobody really knows what became of him. His schoolbag was found in a lane close to his house six days after he went missing, even though the lane had already been searched by gardai. It is suspected that somebody, possibly a child, found the bag elsewhere and left it in the lane but was afraid to come forward with vital information.

Gardai believe Philip is dead and the investigation will remain open until his remains are recovered.

SOPHIE TOSCAN DU PLANTIER

French film maker Sophie Toscan du Plantier fell in love with the remote countryside in Schull, west Cork, and bought a holiday home there. The 38year-old's life ended in tragedy when she was discovered battered to death on 23 December 1996.

A man living locally, freelance journalist Ian Bailey, was immediately identified as the prime suspect in the savage murder and was arrested but never charged with her killing. Bailey had a history of violence against women but a witness who placed him close to the murder scene withdrew her statement.

There are no obvious suspects, according to gardai, who believe that somebody living locally was responsible. The manner in which the investigation was conducted has already been the subject of a review by a team of gardai but the evidence is likely to be re-examined by the new cold-case unit.

RAONAID MURRAY

Raonaid Murray was 17 when she was stabbed to death after a night out on 4 September 1999. She left her friends at around 11.30pm and walked in the direction of her home in Glenageary. The student was seen by witnesses arguing with a man at 11.55pm and a local woman heard a scream soon afterwards.

Raonaid was stabbed four times with a oneand-a-half-inch knife in a lane close to her home.

The garda investigation of the murder has been one of the biggest in memory but it failed to trace her killer. There were half a dozen suspects but their alibis checked out and there has never been a breakthrough.

Gardai believe that a 'Noel Gallagher lookalike' seen around the area murdered Raonaid and possibly left the country on a ferry. Over 8,000 people were interviewed and over 3,000 statements were taken during the original investigation.

STEPHEN HUGHES-CONNORS

The unsolved killing of Stephen Hughes-Connors was one of the cases looked at when the new cold-case system was piloted 18 months ago. The review is still continuing; it has already resulted in one arrest and over 300 people have been reinterviewed.

Twelve-year-old Stephen was sleeping over with a friend in a hut made of wooden pallets and carpet when it was set on fire in the early hours of the morning on 1 September 2001. Stephen had told his parents he was staying at a friend's house. He didn't make it out of the "re although his friend managed to escape.

A man was captured on CCTV footage running away from the scene but he was never caught. A 45-year-old was detained for questioning in April 2006 but was released without charge. He was always regarded as the prime suspect. The case will be transferred to a larger team of gardai when the cold-case unit is up and running in a few months.

MARY BOYLE

Six-year-old Mary Boyle is officially the person who has been missing in Ireland for the longest time. She vanished from her grandparents' farm in Cahelard, near Ballyshannon, Co Donegal, on 18 March 1977. She had been following her uncle across a field but turned back and never reached home. Huge searches were immediately conducted around Donegal but the youngster never turned up and there were no positive sightings of her.

One suspect has been mentioned as possibly being involved in the Boyle case.

Fifty-nine-year-old Robert Black was questioned two years ago by the PSNI about the murder of a young girl in 1981. Nine-year-old Jennifer Cardy from Co Antrim disappeared as she cycled to a friend's house and her body was found six days later. Black is serving 10 life sentences for the murder of three young girls in the UK. Despite his links to Ireland around the time of Mary's disappearance there is nothing to tie Black to the crime and it remains unsolved 30 years on.

ANNIE MCCARRICK

During the 1990s six women simply disappeared without a trace, leaving detectives fearing they were dealing with a serial killer. None of these women has ever been found and it is thought that one man was behind at least four of the disappearances. The prime suspect, convicted rapist Larry Murphy, has never been linked to the crimes.

One of the best-known of Ireland's missing women is American Annie McCarrick, who disappeared in March 1993 after leaving her home in Sandymount. She was seen boarding a bus to Enniskerry. The 26-year-old was reportedly seen with a man near Johnny Fox's pub in Glencullen but this sighting has never been confirmed and no trace of Annie has ever been found.

Operation Trace was launched to reinvestigate the kidnappings but it was not successful. The cases of the other missing women . . . Jo Jo Dullard, Deirdre Jacob, Fiona Pender, Fiona Sinnott and Ciara Breen . . . are all likely to be reviewed as cold cases.