A 17-year-old was stabbed in the chest after he tried to escape a gang of youths who turned up at a party in Harrow after it was advertised on social media site Instagram.
Mr A was among eight young people charged with murder at the Central Criminal Court, in London.
He hired Stuart Miller Solicitors to fight his corner after denying any role in the killing.
A spokesman for the London-based firm said: “The client accepted being with the group on the day of the murder, but he maintained that he was not a participant in the murder.
“Stuart Miller Solicitors spent numerous hours with the client obtaining his instructions and preparing him for trial.
“The team extensively prepared his defence, which included the consideration of over 10,000 pages of evidence and hours of studying CCTV evidence.”
Prosecutors claimed Mr A was part of the gang and presented CCTV evidence showing the route the defendants took.
They also put forward mobile phone data to pinpoint the whereabouts of the eight suspects.
To counter this, Stuart Miller Solicitors enlisted two expert witnesses, including a forensic expert who was able to dispute the prosecution’s CCTV analysis.
An expert pathologist also gave evidence in court in favour of Mr A, who had no previous convictions.
Following a 14-week trial, during which prosecution witnesses and co-defendants were quizzed over Mr A’s alleged involvement by barrister Charlie Sherrard, QC, he was found not guilty of murder.