DNA profiling has in recent years led to the conviction of killers and other serious offenders who, without the union of scientific advance and dogged detective work, would probably still be at liberty. Each such conviction serves justice, satisfies investigating officers and gives the families of victims a prospect of moving on in their lives. But the outcome is not always as the police, families and the Crown Office as prosecutor would hope. The collapse yesterday of the trial of Angus Sinclair, a convicted killer and serial sex offender accused of the so-called World's End murders in Edinburgh in 1977, is one such case.

DNA profiling has in recent years led to the conviction of killers and other serious offenders who, without the union of scientific advance and dogged detective work, would probably still be at liberty. Each such conviction serves justice, satisfies investigating officers and gives the families of victims a prospect of moving on in their lives. But the outcome is not always as the police, families and the Crown Office as prosecutor would hope. The collapse yesterday of the trial of Angus Sinclair, a convicted killer and serial sex offender accused of the so-called World's End murders in Edinburgh in 1977, is one such case.

The Crown believed there was sufficient evidence to proceed to trial and to have a reasonable prospect of a conviction. However, Lord Clarke, the trial judge, concluded that the evidence was, at best, neutral concerning Sinclair's alleged involvement in the murders and dismissed the case. The decision was a blow to the families of Christine Eadie and Helen Scott, the victims, and the source of immense disappointment among officers from Strathclyde and Lothian and Borders police forces who had worked long and hard on these cases and three other unsolved murders.

The reputation of the Scottish criminal justice system relies more than anything else, perhaps, on the principle of the right to a fair trial being upheld. Lord Clarke might well have been correct in ruling that the DNA evidence against Sinclair was not sufficiently conclusive to put to a jury in a murder trial. The result, while frustrating the families and the police, demonstrated that the cornerstone of the system remained in place. The Crown could not pass the test of proving its case beyond reasonable doubt.

The outcome leads on to questions about the advisability, indeed the feasibility, of proceeding with cases that are 30 years old or more. This would not be possible, other than when a voluntary confession is made, without DNA profiling against an expanding database of samples. How widely the net should be trawled is a matter of controversy, as is the quality of the DNA itself. It is only in recent years that measures have been put in place to ensure the potential of DNA to solve cold crimes is not compromised by contamination.

Aside from DNA, the Sinclair trial raises questions about the way the Crown prosecuted the case. It was built on science that fell short of the requirement to convict. A senior source at the centre of the Strathclyde Police investigation into three unsolved murders, also in 1977, today tells The Herald that the prospects of a conviction would have been better had circumstantial evidence, based on the Moorov doctrine linking an accused with a series of crimes, also been led in the Sinclair trial. That investigation has exposed a potential miscarriage of justice. The source maintains the three Strathclyde murders were not added to the case against Sinclair because of the risk of a conviction resulting in just such a miscarriage, which he said would have been unpalatable after the Shirley McKie case. This adds a political dimension to the allegations and they should be investigated as a matter of urgency.

While Lord Clarke's decision reinforced the integrity of the criminal justice system, the jury is out on the Crown Office's handling of this case. It took many years to come to court. Millions of pounds were spent on the investigation. It consumed the time and effort of many dedicated police officers. Yet the Crown went to court with evidence that was found wanting and was thrown out. For the families of the victims, there is still no justice.