The serial killer's calling card is what makes the investigations of his murders so frustrating. "The one thing that marks him out is his ability to get rid of the body -- which usually leaves us with no forensics, DNA or MO [modus operandi]," says Brian McCarthy, a veteran private eye who has been on the trail of one alleged killer for nearly ten years, on and off.

McCarthy was hired by the family of missing American student Annie McCarrick. He suspects that one man was responsible for the disappearances of McCarrick (26) and at least two other women, Deirdre Jacob (18) and Jo Jo Dullard (21).

All three were of a similar age and were last seen on their own, in a triangle between Kildare, Wicklow and Dublin. "There is linkage there, but no physical evidence -- not even a piece of clothing," McCarthy told The Sunday Business Post.

The serial killer theory was scoffed at when Gardai originally began investigating the disappearance of McCarrick in the Dublin Mountains back in March 1993. "It just wasn't considered," a source says.

McCarrick, a New York literature student, was one of the first to vanish in the so-called murder triangle. When her father John McCarrick, a retired policeman, went to a Garda station to report Annie missing he was highly critical of his experience.

The officer who dealt with him did not have a notepad beside him, so he wrote the details on the back of his hand, according to McCarthy.

It was not until the family lobbied the American ambassador, Jean Kennedy Smith, that the Gardai agreed to widen their enquiries five years later.

Operation Trace, based in Naas Garda Station, identified seven other missing people who fitted a similar disturbing pattern.

These were young women, all from Leinster, of a similar age, leading busy, seemingly happy lives until they vanished without trace. They were not victims of suicide, accidents or organised crime. The apparent clinical disposal of their bodies was the most troubling feature of all.

Detectives say that even among the practised shooters operating in the underworld, there has never been a more surgical killer at work in Ireland, outside of paramilitary organisations.

"The facts speak for themselves," says retired detective inspector Gerry O'Carroll. "For decades we had virtually no missing women; now we have up to ten in a relatively small area around the east coast, with various common threads.

"I believe these women were victims of one or two serial killers working together."

O'Carroll, who is now head of security for TNT in Dublin, looked at the missing women's cases as part of the probe into the 1999 slaying of Dun Laoghaire schoolgirl Raonaid Murray (17).

He is now convinced that the suspected murders of Jacob and McCarrick are linked with those of Fiona Pender (26) in Co Offaly in 1996, Ciara Breen (17) in Co Louth in 1997 and Fiona Sinnott (19) in Co Wexford in 1998.

Garda sources on the Trace investigation say every detail about the missing women was fed into a serial killer profile system set up in the British National Crime Faculty in Bramshill College, Lancashire, England. The Violent Crime Linkage Analyses System (VCLAS) also examined other unsolved murders of women around the country.

VCLAS is used to compare eyewitness descriptions of a suspect and vehicle with a victim's address and vehicle details. It then builds a dataset containing profiles of the suspect, the victims and the incidents. This information is fed into a programme that selects and maps the names and addresses -- current and previous -- of those suspects whose modus operandi fits the crimes being investigated.

Gardai also used a geographic profiling facility during the visit to Bramshill College. This relatively new field of environmental criminology analyses the spatial patterns of serial crimes, and maps out the most probable location of the suspect's home.

It works on the premise that most serial criminals operate close to home.

Police say geographic profiling can approximate the location of the offender's home by analysing the spatial patterns of the attacks.

It traced one serial killer to within two-fifths of a mile of his home.

The system, developed 12 years ago by Canadian Detective Inspector Kim Rossmo, is based on research which found that the way African lions hunt matches almost perfectly with the hunting typology of the serial killer.

Lions look for an animal that exhibits some indication of weakness -- the old, the very young, the infirm, the vulnerable. They go to a watering hole and loiter, because they know it is a draw for their potential targets.

"We see that all the time with criminal offenders," says Rossmo. "They go to target-rich environments to do their hunting. Spatial patterns are produced by serial killers as they search and attack.

"The system analyses the geography of these, the victim encounter, the attack, the murder and body dumpsites."

Garda sources said that the profiling system found no definitive link between any of the missing women cases.

Operation Trace still retains a liaison officer in Celbridge Garda Station, and an informed source says that a suspect has recently been identified in connection with Jo Jo Dullard (21).

The 21-year-old Co Kilkenny woman was last seen making a call from a public phone box in Moone, Co Kildare on November 9, 1995. A man from a Traveller background is the new suspect.

"He has moved the body. That is the information we have from an informant," says the source. The possibility that this man was behind the deaths of the other women is being investigated.

There are other suspects: people who knew Patricia Furlong, Fiona Sinnott, Fiona Pender and Ciara Breen.

Opinion is divided among gardai on the serial killer theory. Some detectives claim that there is a rational explanation for each disappearance. Others agree with Gerry O'Carroll and Brian McCarthy's gut feeling that there are too many common denominators here -- and no bodies.

If the lion hunter theory can be applied, the Leinster serial killer's prime hunting ground is the Dublin Mountains, and his first victim may have been Patricia Furlong (23).

Furlong's body was dumped in the mountains only a few miles from Glencullen in July 1982. She had been abducted, raped and strangled. The late DJ Vinnie Connell was convicted of her murder ten years later, but the case was quashed by the Court of Criminal Appeal.

Almost five years to the day that Furlong died, Clondalkin mother of two Antoinette Smith (27) vanished after attending a David Bowie concert at Slane Castle in Meath. She had returned to Dublin and gone to the Harp Bar on O'Connell Bridge before going on to a disco in Parnell Street.

Her body was found nine months later in the Dublin Mountains when ramblers discovered her remains in a shallow grave. She had been raped and strangled. Her head was reported to have been covered by a plastic bag.

Three years later, on the same stretch of mountain bog where her body was concealed at Glassamucky Breakers, Kilakee, a man out cutting turf found a woman's hand in the turf bank he was clearing.

It belonged to Patricia Doherty (30), a mother of two, from Tallaght. Doherty was last seen alive six months earlier when she left her home to do some Christmas shopping on December 23, 1991.

Fifteen months later Annie McCarrick vanished after visiting Johnny Fox's pub in the Dublin Mountains, not far from the graves of Antoinette Smith and Patricia Doherty.

Brian McCarthy, the private eye, suspects that at least two other missing women, Jo Jo Dullard and Deirdre Jacob may also be buried in the mountains.

His prime suspect is a married man with children who can be placed in or around the scenes where Dullard, Jacob and McCarrick went missing. This man has a history of sexual violence against women, says McCarthy. He is currently in prison.

The case against the suspect is far from conclusive, he admits. However, he has little doubt that all three disappearances are linked.

A former boyfriend of McCarrick, Philip Brady, hasn't given up hope that the killer will make a mistake. "If there is a baddie -- and she was slain -- then sombody will make a mistake," he said.

Brady, originally from Monastery estate in Clondalkin, went out with Annie while she was studying in Maynooth College. "It's an understatement to say I think about her a lot. We went out together for four or five years. What's happened has taken its toll. I think about her a lot.

"I'm one of only four or five people who knew what she was really like. She was very deep. There's a funny idea I have that one day Annie will just walk into Dublin Airport alive and well. I know it's very unlikely.

"I hope it's linked, because then there's a chance he will make a mistake, or his wife or his girlfrend will," he says. "I hope and pray every day they will find the fucker behind it."

Are the missing women connected?

Antoinette Smith (27)

From Clondalkin, Co Dublin, raped and strangled in the Dublin Mountains in July 1987

Patricia Furlong (23)

Raped and murdered in July 1982 at Glencullen in the Dublin Mountains

Patricia Doherty (30s)

Murdered and buried in a peat bog in Kilakee in the Dublin Mountains in December 1991

Eva Brennan (40)

From south Dublin, disappeared after leaving her parents' home in Terenure to return to her flat in Rathgar in July, 1993

Annie McCarrick (26)

New York-born student, vanished on March 3, 1993. Last seen in Johnny Fox's pub in Glencullen in the Dublin Mountains

Deirdre Jacob (18)

Last seen walking to her home in Roseberry, Newbridge, Co Kildare on July 28, 1998. The trainee schoolteacher was described as a very balanced person. "The trail has gone cold now, and the prospects of finding out what happened to her are grim," one officer said.

Jo Jo Dullard (21)

Vanished after making a call from a public phone box in Moone, Co Kildare, on November 9, 1995. She had phoned a friend to say she was hitching a lift from there to her home in Callan, Co Kilkenny. A short time later a woman answering Jo Jo's description was seen leaning in the back door of a dark-coloured Toyota Carina-type car. The driver of this car has never been traced.

Fiona Pender (26)

From Tullamore, Co Offaly, she was seven months pregnant when she disappeared on the evening of August 23, 1996. She was last seen leaving the flat she shared with her boyfriend in Church Street in the town. She had spent the previous day, Sunday, shopping for baby clothes and was in good spirits.

Fiona Sinnott (19)

From Bridgetown, Co Wexford, she was last seen leaving a pub in Broadway, Wexford, on the night of Monday, February 9, 1998

Ciara Breen (17)

She disappeared from her home of Batchelors Walk, Dundalk, in the early hours of Thursday, February 13, 1997. She took no possessions with her.