A solicitor has been convicted of smuggling a letter out of Belmarsh jail, which would have provided a gunman with a false alibi.
Maya Devani had visited her client, Timothy Merchant, who was being held on two charges of attempted murder.
But when she left the south-east London prison, she allegedly took written instructions for an alibi.
Devani, 26, of Harrow, north London, was convicted of perverting the course of justice and will be sentenced later.
Merchant, who has since been convicted of the charges, shot two men who gave evidence against his younger brother in a trial.
Days after his brother was sentenced to nine years for an armed raid at a convenience store, Merchant shot one of the witnesses as he sat in his car. His friend was also shot.
When Merchant, 29, from Chelsea, realised an important piece of evidence allegedly linking him to the attack was found in a car, he recruited his solicitor to help him.
But Devani told the court she did not know what was in the letter until she was charged and said she had no reason to put her career at risk to help Merchant.
The Law Society said Devani, who was working for Arani & Co at the time, will face a disciplinary hearing.