When the case against the four men accused of being responsible for his death was heard two years ago, evidence from the then state pathologist, Professor John Harbison, indicated that Murphy died as a direct result of being kicked in the head during an assault. One of the four men was cleared, while two were convicted on lesser charges. The remaining defendant, Dermot Laide, was identified as the assailant whose actions killed the 18-year-old. Laide was found guilty of manslaughter . . . a conviction that was later overturned on appeal.

Last week, however, the current state pathologist, Dr Marie Cassidy, painted a different picture, claiming that the assault on Murphy was "relatively minor." Murphy, she claimed, died of "alcohol-induced apnoea." The case against Laide collapsed.

For the Murphy family there is the pain of having nobody held responsible for their son's tragic death. For the Laide family there is the possibility that their son never would have faced a manslaughter charge if Cassidy had conducted the post-mortem instead of Harbison. For everybody involved, there is a litany of unanswered questions.

1. How did Brian Murphy die?

Until now, it was accepted that Brian Murphy died as a result of a brain haemorrhage brought on by an assault outside Anabel's nightclub. During the original trials of the four men accused of taking part in the assault, the jury heard that Murphy was on the receiving end of a short but vicious assault, during which he was repeatedly punched and . . . crucially . . . kicked in the head. Marie Cassidy's intervention last week, however, has cast doubt on that.

According to Cassidy, Murphy received "relatively minor" injuries, which "would not be expected to cause his death." What killed Brian Murphy, she claims, was alcohol-induced apnoea, or a stopping of breathing. It was apnoea, and not the assault, that caused the brain injury that killed Brian Murphy.

2. Did anybody kick Brian Murphy in the head?

According to the report filed by Cassidy, "the skull was not fractured and there was no evidence of bleeding into the skull cavity". However, during the trial, Harbison said Murphy was most likely killed by a kick to the head. Of the four men accused, three . . . Dermot Laide, Desmond Ryan and Sean Mackey . . . admitted to having either punched or kicked the victim in the body.

The other accused, Andrew Frame, was found to have had no role in the assault.

Several witnesses reported seeing a male kick the victim in the head as he lay on the ground. However, the description of the assailant did not match any of the accused. Even if the kick to the head did not kill Murphy, it seems likely that at least one other man . . . and, in all likelihood, several . . . played a role in the assault, with one possibly having kicked the victim in the head.

3. Is Marie Cassidy's report as reliable as John Harbison's initial post-mortem?

Cassidy conducted her report without access to Harbison's initial notes, as the DPP's office believed they might compromise the independence of the second probe. However, she did have access to post-mortem photographs and toxicology and histology records gathered by Harbison. The Scottish system of using two pathologists in cases of violent death would have meant that both would have attended the initial post-mortem. There is no way of knowing whether Harbison's or Cassidy's findings would have been amended had this occurred in the Brian Murphy case.

4. Did Murphy drink enough to induce apnoea?

Apnoea, the temporary cessation of breathing, is heightened by alcohol, which depresses breathing reflexes, although it is not brought on by the drinking of alcohol.

What Cassidy asserts is that Murphy received a concussion during the fight, which brought on apnoea. This condition was then worsened by the level of alcohol in his blood stream. The alcohol, mixed with the effects of concussion, stopped his breathing long enough for the brain to die.

5. Why was a manslaughter charge brought against Dermot Laide?

Dermot Laide questioned whether the state would ever have brought a manslaughter charge in the Murphy case had Cassidy's report been available from the beginning. Laide admits he was involved in a fracas. He was convicted and sentenced in March 2004 to four years.

Though there was little evidence to link him with kicking Murphy, presiding judge Michael White said he was "satisfied that Laide's actions contributed substantially to the escalation of the row which led to Murphy becoming surrounded and defenceless." He said the aggravating factors against Laide were the death of a young man, the grief of his family, his contribution to the escalation of the dispute and the "use of violent force completely out of proportion to the situation he faced, when he was not personally threatened." Laide's conviction was overturned on appeal.

6. How reliable were the witness statements?

Many questions remain regarding the reliability of much of what was heard in court prior to Laide's initial conviction, largely because a large amount of alcohol was consumed on the night of the row by many of those who later became witnesses in the court. Brian Murphy himself had seven or eight pints. One witness described himself as being "quite tipsy" after having had four pints, a couple of Smirnoff Ice bottles, five cans and a naggin of vodka. Another admitted to having six cans of Amstel, three or four pints of Budweiser and a few sambucas. Many of those who gave evidence had been at Anabel's nightclub, where Smirnoff Ice was having a £2 drinks promotion.

7. Was Dermot Laide central to the row in which Murphy died?

As well as the manslaughter charge, which was later overturned, Dermot Laide was convicted of violent disorder, for which he was sentenced to two years. The court heard that he was centrally involved in a general melee that developed among a large number of young men outside Anabel's nightclub that night. Laide has never contested this. In his statement last week following the DPP's decision not to retry the case, Laide publicly said he wished to acknowledge that his behaviour on the night was "totally unacceptable." He added: "My conviction for violent disorder is valid, and I wish to sincerely apologise to all those who have been hurt or affected by my actions or the fall-out from them."

8. How many people were involved in the assault?

Witnesses report seeing six men involved in the attack on Brian Murphy. Considering Andrew Frame was found to have played no role in the assault, this means that at least half the assailants were possibly never charged. The fight broke out when Murphy punched Frame after what was believed to be a row over a female companion. Several men, including Laide, Mackey and Ryan, then intervened. Due to conflicting witness reports, the number of people involved was never proved. The identities of the other men alleged to have taken part were never revealed.

9. Will last week's events affect other cases?

The impact of last week's events on other criminal cases remains unclear. There are two issues which could have a knock-on effect. First, John Harbison is no longer able to appear before the courts due to health problems. This means that the former state pathologist would be unable to testify in any retrials of cases in which he was involved. Harbison was involved in at least four manslaughter cases similar to the Brian Murphy case between 2000 and his retirement in January 2003. However, in those cases the defendant pleaded guilty and so the convictions will not be appealed.

The second issue that could affect future trials relates to Cassidy's reading of the injuries sustained by Murphy. While defence lawyers may be likely to claim alcohol-induced apnoea in future cases, each case will have a different degree of assault.

10. Will anyone ever be charged with Brian Murphy's killing?

The state could retry Dermot Laide as the DPP entered a nolle prosequi . . . effectively a suspension of proceedings . . . but given the conflicting pathology reports this is not likely. The character who was identified in court as having delivered a serious kick has never been revealed. This person's appearance and attire . . . spiky hair and shoes with a silver belt buckle . . . was dramatically different to anything worn by Laide, Ryan, Frame or Mackey on the night. Cassidy's report states that death was a consequence of Murphy's own alcohol consumption combined with 'minor" trauma. Such a conclusion makes it almost impossible for the state to pursue a manslaughter charge in future against anyone in this case.

State pathologist's conditions 'unbelievable' ITIS a crucial cog in the wheel of justice, on which a prosecution can stand or fall. Using expert medical opinion and technology, its conclusions can mean the difference between conviction and acquittal. So why does the state's pathology service operate from a cramped office on the grounds of a fire brigade training school in Dublin?

The government has long been accused of neglecting the Office of the State Pathologist.

Although plans were unveiled two years ago to build new offices for the pathology service, they have yet to be carried out.

The Dublin office, which employs a pathologist, a deputy pathologist, a senior scientist and three clerical staff, has an annual budget of /550,000.

The office was in Trinity College for many years after its establishment in 1974 but has for the past several years been housed at the Dublin Fire Brigade training centre in Marino.

What has emerged in the past week is a picture of a service which has remained underfunded since its inception, and which saw the former chief state pathologist, Professor John Harbison, working without any assistance and under circumstances which would not be acceptable in any area of private medical practice.

It was not until 1997 that Harbison's workload was reduced by the appointment of a deputy state pathologist, Dr Marie Cassidy. She took over from her predecessor in 2003 on Harbison's retirement. But the picture before that is one of some chaos and disorganisation.

One academic working in the science field, who did not wish to be named, last week told the Sunday Tribune how he was once drafted in to conduct a postmortem when Harbison was out of the country, before Cassidy's appointment.

"I was contacted by the investigating garda and I said I couldn't do it, I was not a forensic pathologist, I couldn't and shouldn't be doing it. I was called by a senior garda again and after a lot of pleading on his part I consented. There wasn't anybody else to do it, but the entire thing was very distasteful and I did not in the least enjoy the difficult time I received later in court [at a criminal trial related to the death]. What John Harbison put up with for years was unbelievable."

Despite the importance of forensic pathology reports in major criminal cases, including murder and manslaughter, Cassidy has consistently explained that their findings should not be taken as absolutely or unquestionably correct. Debunking some of the mythology over how exact forensic pathology is, Cassidy said in a speech last week: "If your whole case rests on one witness. . . and that witness is a forensic pathologist. . . you'd have a shaky case."

While Cassidy declined to answer media questions related to last week's controversial turn in the Brian Murphy case, she made one comment that would have resonated with Brian Murphy's mother.

After the state entered a nolle prosequi in the prosecution of Dermot Laide over the death of Brian Murphy, Mary Murphy last week publicly claimed that the second pathology report on her son's death, conducted by Cassidy, should have been tested in court.

Cassidy told her audience at Dublin City University's nursing school that guilt or innocence is a matter for a jury to decide, irrespective of how sound any forensic pathologist's findings appear to be. "It is not up to me to decide whether someone is innocent or guilty, " Cassidy said.