A LONG awaited forensics report into the case of a man acquitted of murdering a gangland figure in a supermarket car-park murder has been labelled a "whitewash".

Ross Monaghan walked free from the High Court in Glasgow after being cleared of shooting dead Kevin "Gerbil" Carroll, 29, as he sat in a parked car outside Asda in Robroyston six years ago.

Trial judge Lord Brailsford issued a damning ruling on the forensic evidence as he cleared father of two Mr Monahan in May 2012. It emerged a minute quantity of father of two Mr Monaghan's DNA was found on the handle of one of the guns used to kill Carroll.

The DNA of a lab technician who had never touched the gun was found on a sample along with that of three unidentified men.

In its report on the case, the Forensic Science Regulator found there was "nothing inherently wrong" or "improper" with the actions of the scientists involved - a finding a senior lawyer who attended the court proceedings claims is a cover-up of what really went on.

The row centred on a single particle of firearms discharge residue found on a jacket seized during a raid on Mr Monaghan's home.

Forensic expert Alison Colley, who worked for the Scottish Police Services Authority, now the Scottish Police Authority (SPA), said the particle was insufficient to draw any scientific conclusion, despite previously preparing a report which appeared to state it was a similar type to that found in cartridges at the crime scene.

She admitted in court this opinion rested on tests which she would not normally perform, but which a detective in the case had "pressured" her into carrying out.

Ms Colley also revealed she was unaware that firearms officer, who had been on a gun training exercise earlier that day, were involved in the search on Mr Monaghan's property, posing a risk of cross-contamination.

Judge Lord Brailsford went on to rule that the evidence was inadmissible.

The senior legal source, who did not want to be named, said: "This report is a whitewash. We have a judicial finding that pressure was put on a scientist to change her report.

"She and her colleague both say they were pressurised by police, that they tried to tell them comparing a single particle had no evidential value - these are the words that they used, both in court and to the regulator, yet there's nothing improper with that?

"The judge saw her give evidence in court, he saw her demeanour, and, with years of court experience, took all that into account and ruled this piece of evidence was inadmissible."

The regulator's report features court testimony by Ms Colley - including the judge questioning her on why she did not refuse the detective's request.

She replied: "We have tried... on a number of occasions giving out advice and saying we advise against something or not, and sometimes we're overruled and told just to do it."

However, the regulator found the comparison between the particle and the cartridges "would not routinely be performed, but was not prohibited".

On the issue of firearms officers attending the search, the report says both scientists were clear that, had they known, they would have given advice that the risk of contamination would make the already weak evidence "even weaker".

It would also have led to a statement in their report about the risks of such contamination being the source of the particle on the jacket.

The regulator recommended that the SPA review its procedures to reduce the risk of scientists being left in the dark like this again.

The authority has also been urged to adopt a policy of providing clear statements on the evidential significance of a single particle of firearms residue.

Forensic expert Professor Allan Jamieson, of the Forensic Institute, argued the report is "neither sufficiently focussed nor sufficiently critical".

He said: "The expert is expected to be 'the independent product of the expert uninfluenced as to form or content by the exigencies of litigation'. In this case, it clearly and admittedly was not."

He added: "Ms Colley is to be congratulated for her openness and honesty in disclosing the process, but she and the SPA have to accept responsibility for a culture in which this could happen and remain undiscovered until the court."

Following Mr Monaghan's acquittal in 2012, William Paterson was convicted of Mr Carroll's murder last year

The regulator's report could not be released while his proceedings were ongoing.

An SPA spokesman said: "The Forensic Regulator is the foremost independent voice on the integrity of the science in the UK. We respect its findings and rest on the weight of its evidence base and authority.

"Its report represents in our view the most informed and dispassionate view on the circumstance of the case, and a reassuring one for the integrity of the individuals and organisations concerned."

Police Scotland said it noted the report's publication.