Elish Angiolini, the Lord Advocate, has raised the prospect of a change in the law which would allow the Crown to appeal certain criminal cases if they are thrown out of court.
In a passionate statement to parliament yesterday in wake of the case's dramatic collapse, she said such a right of appeal could hypothetically have been used.
Earlier in the day Alex Salmond, the First Minister, said ministers were also considering scrapping "double jeopardy", the legal principle which prevents people being tried for the same crime twice.
The controversial changes would form part of a criminal justice bill due to come before parliament next autumn.
Angus Sinclair, 62, a convicted killer and sex offender, was accused of murdering two 17-year-old girls last seen in the Edinburgh pub 30 years ago.
However, on Monday the judge ruled there was insufficient evidence to proceed with the case.
The decision led to angry recriminations from the families of the young women and accusations that the prosecutors had bungled the case. It also led to calls for a change in the law so that the Crown could ask another judge to put the case before a jury and for a re-trial should new evidence emerge.
Yesterday Ms Angiolini faced the public over the trial. She argued there was "sufficient evidence" to take the case to a jury and if the law was changed the Crown would have tried to appeal the judge's decision.
Discussions with Kenny MacAskill, the justice secretary, have already begun about changing the Crown's right to appeal, she confirmed.
However, there were concerns about a "knee-jerk" response to the high-profile murder trial leading to reckless changes in the law. Reports that not all the possible evidence was used by the prosecution and also that police wanted to try Sinclair for other murders, stoked concern from the public.
Yesterday, Ms Angiolini's statement attempted to defend the Crown's position.
She said: "I am of the clear opinion that the evidence made available to the court was sufficient to be put before the jury to allow them the opportunity to decide on the case against Angus Sinclair."
In graphic descriptions, she laid out to parliament the prosecution's case including the claim that Sinclair's DNA was found on both women. And she defended the prosecution service against "armchair commentators".
Ms Angiolini explained the reason certain evidence, which was DNA from Sinclair on underwear used as a ligature, was not presented because there was already stronger evidence that Sinclair had sex with both women.
She went on: "I would like to make clear that the Solicitor General and I are of the view that even if the advocate depute had chosen to lead the evidence in relation to DNA on the ligatures, given the way in which the judge approached the case it is unlikely to have persuaded him to repel the defence submission. The judge considered that there was evidence of sexual contact between Angus Sinclair, Christine Eadie and Helen Scott, but he took the view that no further inferences could be drawn from that evidence.
"In his view the evidence of sexual contact was neutral as to whether or not Sinclair was involved in using violence or force against the girls, and neutral as to whether Sinclair was present when the actions of violence and force took place."
Her statement also disclosed that prosecutors had previously considered the possibility of Sinclair being responsible for the murders of four other young women in Glasgow in 1977.
But in those cases there was no DNA evidence, no confession, and no direct evidence.
When MSPs asked if she would have appealed the case if the Crown had right of appeal, she answered: "Clearly from what the Crown submissions were at the conclusion of the case and given what I have said about the submissions, it would have been the case [that] the Crown would have appealed should they have been able to."
Mr MacAskill confirmed there had already been discussions in cabinet about the crown's right of appeal.
He said: "Under powers that exist south of the Border and elsewhere - if there is a judicial decision such as the World's End case, where the Crown feels the wrong decision was come to, they have a right of appeal. I am broadly sympathetic about that but it is not straightforward, we have to be considered."
Kevin Scott, the brother of Helen Scott, said the law needed to be reconsidered. He said: "Something has gone wrong. We do not have justice under the current law. We will never have justice."
Earlier in the day Mr Salmond faced questions from MSPs clearly motivated by the conclusion of the World's End trial.
Cathy Jamieson, the acting Labour leader, spoke of a "a growing mood" to scrap double jeopardy in Scotland after the case.
"There are questions that are for politicians and not for prosecutors," she said.
In reply, Mr Salmond indicated he would be in favour of scrapping double jeopardy.
"I think there is a range of lessons we can learn from recent events in the judicial system in Scotland," he said.
A spokesman for the First Minister said later: "His point of principle on this is not to have a knee-jerk reaction in relation to any particular case. He has stressed the need to look at more than just that issue, and to look at things in a considered fashion."
Mr MacAskill said ministers were also considering ending double jeopardy.
He said: "There do appear to be instances where new technology and scientific matters clearly show an injustice was served.
"It is not about bailing out the Crown for a failure but if information is uncovered like new DNA or that witnesses were intimidated, it does seem to me justice should allow prosecution [to make] the argument."
The Tories also backed the move. Paul Martin, the Labour back-bencher, is trying to bring in a member's bill to scrap double jeopardy.
But Patrick Harvie, the Green MSP, warned against scoring points on the back of a "high-profile and deeply distressing case".
"This is a time for careful and thoughtful reaction, not a knee-jerk response designed only to sound tougher on crime than one's political opponents."
• Additional reporting by Michael Howie
'Legal shake-up is long overdue - and hopefully it won't be too late for us'
MORAIN Scott, the father of World's End murder victim Helen Scott, said last night he would be prepared to go through the ordeal of going to court again if the announcement on the Scottish legal system allowed another trial.
"We've had our death penalty for the past 30 years, but we need to get justice for Helen and Christine. The girls deserve that.
"We had always been led to believe that our legal system was next to none, yet a judge throws out something like this. We always thought the Scottish legal system was the best and would see us right.
"I think the double jeopardy principle should go - at the very least, the prosecution should have the opportunity to appeal because, after all, the defence can do this.
"I would hope any new legislation would be retrospective, so that it is not too late for us."
He went on: "Yes, it's been exhausting mentally and physically, waiting and waiting for this trial. It kills a part of you. You always put a face on it, try to take the weight of it. It's been hard for the families, Christine's parents and ourselves, but we would do it again. For the girls."
The move was also welcomed by Joe Duffy whose daughter, Amanda, a drama student, was murdered in Hamilton.
In 1992 Francis Auld, 19, was tried for her murder and admitted inflicting bite marks on her chest. But he claimed the teenager had been murdered by a man she met later that night, and he walked free after a jury returned a not proven verdict.
The Duffys later won 50,000 damages after raising a civil action against Auld at the Court of Session in 1995.
Mr Duffy, project co-ordinator for PETAL (People Experiencing Trauma and Loss), said: "There should always be a mechanism to overturn a 'perverse verdict' - the guilty should not be able to walk free. There needs to be justice for families of those whose loved ones have been murdered or suffered some terrible attack or sexual assault.
"Francis Auld is walking about free and we have no recourse to that verdict. But if someone says they are wrongly convicted, all hell breaks out and they get a chance to appeal. The victims and families don't have that right."
Of the legal shake-up, he said: "This is long overdue - it is most definitely time it was reviewed. The Scottish legal system needs to have the balance put right."
Mr Duffy said he had little faith in the standing accorded to judges in the Scottish courts.
"Judges appear to be infallible. But they are all human beings and, like everyone else, they make mistakes. But when they make a mistake it is the victims and their families who have to endure years worth of suffering. The last word should not lie with a single judge," he said.
Complex courtroom system
JUDGES have, under Scots law, had the right to throw out a case due to insufficient evidence since time immemorial.
Common law dictates that the court can make a ruling of "no case to answer" after all the evidence has been heard.
For several decades, however, the defence has also had the power under statutory law to make a submission of "no case to answer" at the conclusion of the prosecution case alone.
This was most recently enshrined in the Criminal Procedure (Scotland) Act 1995, and it was this power that the defence used at the end of the prosecution's evidence in the World's End case.
It will require new legislation to enable the Crown to appeal against a specific "no case to answer" decision, which is why the Lord Advocate, Elish Angiolini, has raised the matter with Alex Salmond, the First Minister.
In fact, the Crown already has limited powers of appeal. The prosecution can challenge a ruling by applying for what is known as a Lord Advocate's Reference. However, such a step takes months to conclude and, therefore, is regarded as impractical and only taken rarely on important points of law.
Currently, the Crown's ability to appeal the decision of a judge is restricted to unduly lenient sentences and other matters where the court is thought to have wrongly interpreted a law.
Conversely, the Crown is generally not allowed to appeal "fact-based" decisions of the court. These include "no case to answer" rulings.
Double jeopardy 'safeguard'
THE double jeopardy rule, known in law as autrefois acquit, developed in Britain over centuries as a protection against oppressive prosecution.
Until the Criminal Procedure and Investigations Act 1996 there was an absolute bar on a case being reopened after acquittal. That act introduced certain limited circumstances for a prosecution appeal, for example where the intimidation of either witnesses or jury had affected the outcome of a trial. But no retrials were sought under that provision.
It was the Macpherson inquiry into the murder of Stephen Lawrence which subjected the double jeopardy rule to scrutiny and recommended that prosecution after an acquittal should be allowed where "fresh and viable" evidence was presented.
Such a change was introduced in England, but not in Scotland, where the attitude that removing the principle of double jeopardy would encourage less thorough prosecutions prevailed.
South of the Border, the term "fresh and viable" was changed in 2003 to "new and compelling" evidence.
"New" signifies evidence which could not have been brought forward by the prosecution at the original trial. A retrial cannot be ordered on the basis of evidence that was already available to the prosecution at the first trial, but which was not presented.
"Compelling" means reliable, substantial and appearing highly probative of the case against the acquitted person.