A gang member who drew “childish doodles” of a brutal and random killing he planned to carry out has been jailed along with three others in his crew.

David Gomoh, a 24-year-old NHS worker, was stabbed to death as part of a “meaningless feud” that sparked a “petty but fatal game of one-upmanship” played out on the streets of London, the Old Bailey has heard.

The marketing graduate, who worked in NHS procurement, was repeatedly stabbed in the street on April 26 last year as he spoke to his girlfriend on the phone.

He staggered back to his home in east London and bled to death in front of his horrified family.

Jurors heard the victim had nothing to do with gangs but was nonetheless targeted in the ongoing rivalry.

Investigators later uncovered sketches by one of his killers which revealed a chilling “picturebook story” of the events leading up to the murder.

David Ture, 19, of no fixed address; Vagnei Colubali, 22, of Cambridge; Muhammad Jalloh, 19, of no fixed address; and a 17 year-old boy from Telford, Shropshire, were found guilty of Mr Gomoh’s murder on Wednesday.

The defendants were also convicted of conspiracy to cause grievous bodily harm with intent to another man who got away and has never been identified.

Jurors deliberated for almost 15 hours before returning the verdicts of guilty on all counts.

Members of Mr Gomoh’s family attended court in person on Wednesday and gasped as the verdicts were read out.

Speaking outside court afterwards, Mr Gomoh’s sister Lizzie said: “David’s murder is without a doubt the hardest thing my family and I have been through. It is something that no family should ever go through.

“Nothing will bring back a life that was so full of promise and hope, a life that was brutally taken away from us, but we are grateful now that we can begin to mourn.”

The trial had heard how Mr Gomoh was picked at random by the Northside Newham Gang to send a message to rival Custom House and Beckton gangs.

The defendants armed themselves with knives, changed clothes and got a stolen car with false number plates before setting off to south Newham to find someone to attack.

They first chased an unidentified man who managed to run away. Less than an hour later, Mr Gomoh left his home address in Custom House to go to the local supermarket.

He was chatting to his girlfriend on a mobile phone who heard someone demand “where are you from” and sounds of a struggle.

After inflicting multiple stab wounds, the attackers fled in a stolen car driven by Colubali. A pair of sunglasses left at the murder scene were found to have the 17-year-old defendant’s DNA on them.

A second pair of glasses inside the discarded getaway car had Jalloh’s DNA on them.

Police uncovered a series of drawings from Ture’s bedroom showing a number of young men carrying out a stabbing in order to attack one of their rivals.

The sketches not only showed the location of Mr Gomoh’s murder in Freemasons Road but the clothes the defendants had worn.

Detectives said the sketches were a “picturebook story of the events leading up to the murder”, and included detail only the killers would have known.

Senior Crown prosecutor Lousie Attrill said the case “highlighted the tragedy of postcode killings and gang rivalries”.

Speaking after the verdicts were delivered, she added: “These individuals had planned to kill anyone they came into contact with who they believed to be from opposing gangs.

“David was tragically caught in the middle of a meaningless feud. Despite having no connections to gangs he was killed without hesitation.

“The prosecution’s case included CCTV, forensic evidence and drawings made by Ture which were found in his bedroom.

“We were able to show these childish doodles to the jury and the jury convicted the defendants today.”

Mark Lucraft QC, recorder of London, set a sentencing date for September 17.