Mr J was alleged to have made a call to the family of his victim admitting the fatal stabbing.
The conversation, which had been put on loudspeaker, was overheard by a police officer at the victim’s home and recorded on his body camera.
Stuart Miller Solicitors was instructed to represent Mr J, who denied murder.
Prosecutors claimed that Mr J and his victim were childhood best friends but fell out over a drugs debt.
Mr J denied deliberately killing his friend and insisted that he acted in self-defence after being summoned to his home and threatened.
The killing was not witnessed and the murder charge hinged heavily on the apparent phone call confession.
Stuart Miller Solicitors instructed a forensic speech scientist to examine the audio recording.
His findings contradicted the prosecution evidence and a different transcript and expert report was put forward to jurors.
It also emerged that the victim’s phone was never found by police – meaning that vital evidence potentially on the device could not be retrieved.
Stuart Miller Solicitors requested evidence on the phone’s movements after the tragedy to show that the phone had been moved in a bid to conceal its contents from the authorities.
A spokesman said: “This application weakened the Crown’s case and resulted in prosecutors accepting a plea to the lesser offence of manslaughter.”