A 61-year-old mother who got classified information from a police computer in an attempt to assist her jailed son has been cleared of misconduct charges.

Diana Lank wanted to find the identity of an anonymous witness whose evidence helped to convict her son of murder.

Ms Lank was formally acquitted at the Old Bailey after a jury at her re-trial could not reach a verdict.

Two police staff who obtained the information for her were found guilty of misconduct earlier this year.

Diana Lank, who ran a clothes shop in Chelsea, west London, admitted she had received information about a protected female witness, who had testified from behind a screen at the trial of her son Rupert Ross.

The details were held on a confidential police database - but she argued her actions were justified, claiming he had been wrongfully convicted.

Ross, 35, was jailed for life in 2011 alongside Leon de St Aubin, 39, for the killing of Darcy Austin-Bruce outside Wandsworth prison on 1 May 2009.

In Ms Lank's trial, prosecutor Mark Heywood QC, said she wanted to uncover details about a young female witness who said she had seen ex-Dulwich College pupil Ross travelling towards Wandsworth Bridge in a car with two other men on the afternoon of the murder.

Mr Heywood said that the following year Ms Lank orchestrated a "persistent, determined and ultimately successful attempt" to "penetrate the digital criminal intelligence system" of the Metropolitan Police to uncover details that would identify the witness.

Analysis

By Danny Shaw, home affairs correspondent

The question at the heart of this case was how far someone can go to investigate a potential miscarriage of justice. Diana Lank risked going to prison.

She found out the identity of a murder trial witness whose anonymity was protected by court order and whose details were held on a confidential database - security breaches police, prosecutors and judges took extremely seriously, and for which the two civilian police staff now face long jail terms.

But Ms Lank walked free, having argued that her son's fight for justice hinged on unmasking the witness's identity and therefore being able to research their background.

Her actions highlight the difficult balance between protecting witnesses who give evidence anonymously and giving those they are accusing enough information to mount a defence.

Above all, they remind us of an old saying: "A boy's best friend is his mother."

The jury spent eight days considering whether her actions had been justified or not but was ultimately unable even to agree a majority verdict.

Ms Lank was acquitted of conspiracy to commit misconduct in a public office.

A jury at Ms Lank's first trial had also failed to come to a verdict.

Two police detention officers, Lydia Lauro, 33, the girlfriend of St Aubin, and former police community support officer Hayden Cheremeh, 36, were were found guilty of conspiracy to commit misconduct in public office.

They will be sentenced on 20 January.

'Brutal execution'

Ms Lank's trial was told that the killing her son was involved in was a "brutal execution" involving "rival drug dealers".

After the trial, Ms Lank's lawyer Greg Stewart said the case threw up "really serious considerations about how we deal with anonymous witnesses".

"If there is material that suggests that they were not independent and they're being put forward as independent witnesses, the defence has to engage with those issues," he said.

"It creates real problems for lawyers, appellants when trying to suggest to the appeal court there may have been something wrong with the original process."

The Court of Appeal has turned down a legal challenge by Ross and St Aubin against their convictions.

Ms Lank said her son would apply to the Criminal Cases Review Commission to have his case re-examined after fresh information emerged during her court proceedings.