The highest-profile criminal case in which DNA profiling was used was the Miss X case in 1993. In it, a south Dublin man was convicted of raping the 14-year-old girl at the centre of the right-to-travel controversy which convulsed political life for several months during the previous year. The case against the accused was proven on the strength of samples taken from the victim and validated at Cellmark Diagnostics in Oxfordshire, England.

DNA profiling was first used in a criminal case in the Republic in 1987 when a youth was charged with and later pleaded guilty to the murder of Ms Carol Carpenter, a 15-year-old girl who was raped and strangled in Tallaght in August 1988. Her killer was sentenced to life imprisonment and committed suicide in jail in 1994.

The first successful case in which mass screening of suspects took place for the purposes of DNA profiling was in the investigation into the murder of the civil servant, Ms Marilyn Rynn, who was raped and strangled as she returned to her home in Blanchardstown from a Christmas works party on December 22nd, 1995.

After six months of taking samples from more than 200 men and having these analysed, a local man was eventually caught and charged. In January 1998 he pleaded guilty to the murder and is serving life imprisonment.

Until 1994 all DNA profiling in Irish cases was carried out in England. Since then profiling can be carried out at the Forensic Science Laboratory in Dublin, but samples are still sent to England where more sophisticated screening equipment is in use. Between 50 and 100 cases a year are analysed in Dublin, almost all involving sexual assault.

The basic science of DNA profiling has been available since the mid-1980s. It was first used in court in 1985 to prove the parentage of a Ghanaian boy who was refused entry to the UK although his family claimed he had been born in Britain.

His family requested DNA analysis of their son and were able to prove to the authorities - who claimed he was someone else - that he was in fact their progeny. A year later the same process was used to exonerate a youth who was facing a rape charge.

The system, which was perfected by Prof Alec Jeffreys, of Leicester University, has become one of the mainstays in the work of detectives investigating crimes of violence.

Since Prof Jeffreys's initial work, the use of DNA (deoxyribonucleic acid: the chemical carrier of genetic information in human beings) profiling has become highly sophisticated. DNA can be extracted from the tiniest samples of tissue or even hair.

As a result, the primary action in a typical murder investigation now entails the sealing of the crime scene around the body. Crime scenes are often sealed inside tents with police officers and forensic scientists wearing laboratory suits and face masks to prevent pollution of the scene, as microscopic samples of DNA can be used in prosecutions.

The use of DNA in evidence has been possible since the 1990 Criminal Justice (Forensic Science) Act. Under this the suspect must consent to having a sample taken and any sample taken must be destroyed within six months.

This contrasts with the system in other countries such as the United Kingdom where police can compel a suspect to provide a sample - either blood or a mouth swab - and where the DNA profiling information is kept on a national database.

The European Council has proposed that there be Europe-wide standards on DNA profiling for criminal purposes and that there should be a database of DNA information from offenders, which has gained support since the discovery of the ring of paedophile murders in Belgium three years ago. The council's proposals, dating from 1992, are still being considered by the Department of Justice, but there is no proposal yet to have a databank of DNA information on suspected or convicted sex offenders or murderers.

It was not clear yesterday why it had taken so long for there to be DNA analysis of the 300 or so blood samples taken from men in the Kildare area as part of the investigation into the murder of Ms Murphy. The detectives who had investigated the case had a sample of semen from her body.

Although the case preceded the arrival of DNA profiling in Ireland by some eight years, it appears the samples in this case had a low priority in the intervening years and were kept stored in the Technical Bureau at Garda Headquarters.

This situation apparently changed in July last year when another Kildare girl, Ms Deirdre Jacob, disappeared. Her disappearance was accompanied by a major public outcry and major coverage in the media. Some believe she has been murdered and secretly buried.

In the years since Ms Murphy was killed a number of other young woman disappeared in the same general area; they were almost certainly murdered and buried in secret graves.

Gardai could give no explanation yesterday as to why the samples in the Murphy case had remained unexamined for a decade after DNA profiling services were available.