FIELDS and ditches around the victim's house are being searched by gardai looking for the knife used to kill Ms Anne Marie (39) during a sexual assault on Monday morning.
Gardai in Tralee said last night, investigation was "going very well" but could not confirm that a suspect had been identified.
However, they suspect the killer came from the farming area in Tralee, where Ms Duffin lived with her two teenage sons.
Over the past few years a succession of women have been assaulted and killed, either on their way home or in their own homes, band in the majority of cases the victim is known to the killer.
While most killings are solved and the killers brought to court, some remain unsolved. Occasionally, gardai have a firm idea about the killer but are unable to gain evidence to convict.
Garda has only encountered one case in which random killings were the work of potential serial killers. This was the case of Geoffrey Shaw and John Evans, two Englishmen who came to Ireland with the intention of carrying out a series of rape killings of young women in the mid 1970s.
They were caught by gardai, after they had killed two young women and just as they were about the abduct and kill another in Galway.
However, the spectre of a serial killer or killers has arisen in relation to the suspected killing of the young Co Kilkenny woman, Josephine Dullard, following reports that two young men had tried to abduct another young woman in Newcastle, Co Dublin, on March 13th. The woman was able to struggle free as one of the men tried to pull her into a car.
In the Leinster area south of Dublin, taking in the Dublin and Wicklow Mountains, there have been a number of killings of women over the past 20 years.
Annie McCarrick, an American student aged 26, disappeared from her home in Sandymount, Dublin, in March 1993 and was never seen again. There were suspicions that she visited the Enniskerry area and met her killer there.
The body of Marie Kilmartin, a nurse, was found five months after she disappeared from her home in Portlaoise on December 16th, 1993. Her body was found at Pims Road, off the Mountmellick to Portarlington road, six months later. She had been strangled.
Patricia Doherty, a prison officer, disappeared while doing last minute shopping in Tallaght, two days before Christmas 1991. Her body was found in the Dublin Mountains in June 1992.
Antoinette Smith (27) disappeared in Dublin in July 1987 after attending a rock concert at Slane Castle, Co Meath, earlier in the day. Her body was found in May 1988 in a shallow grave in the Dublin Mountains. She had been raped and strangled.
Phyllis Murphy (20) was abducted after leaving a Co Kildare pub in December 1979 and murdered. Her body was found in Dublin Mountains. No suspect emerged in the investigation.
Gardai have still to solve number of other murders women, including that of Rynn (41), the Dublin civil servant who was raped and strangled on her way home from a Christmas party last year, and that Philomena Gillane, shot and left in the boot of her car at Athlone train station in May 1994.
The case of Grace Livingstone, the middle aged woman beaten and then shot dead at her home in Malahide, Co Dublin, in December 1992 remains unsolved.
No conviction was ever obtained in the case of Deirdre Mulcahy, who was raped and murdered at Midleton, Co Cork, in 1989. The main suspect, a 28 year old Cork man, committed suicide last month near Midleton.
The case of Mrs Maureen Stack (38) of Sandycove, Co Dublin, who was beaten to death in her home in November 1985, remains unresolved.
In a number of other cases gardai have been unable to obtain convictions in court.