Two gunmen who shot dead a 15-year-old schoolboy in his bed after mistaking him for his brother are facing life behind bars.

Michael Dosunmu, who wanted to become an architect or a Christian minister, was hit three times in the back as the killers sprayed his bed with fire from a Mac-10 sub-machinegun. Michael, who had celebrated his birthday two days before the attack in February last year, died almost instantly after one of the bullets passed through his heart.

The gunmen, Abdi Omar Noor, 22, and Mohammed Sannoh, 19, were seeking his brother, Hakeem, 26, in revenge over the death of a friend.

Hakeem, a former serviceman, had served with distinction in Iraq and on the UN landmines programme in Bosnia, but after leaving the Royal Engineers he began dealing in drugs and mixing with some of South London’s most notorious gangs.

Noor, a Somali, and Sannoh, from Sierra Leone, were unanimously convicted yesterday of murder by a jury after nine days of deliberation. They will be sentenced today.

Michael’s father Rasak, a psychiatric nurse at Gordon Hospital in Westminster, punched the air and shouted “Yes” as the verdicts were announced. The boy’s mother Shakira, also a psychiatric nurse, paid tribute to her son: “Michael was faultless. The nicest boy you could hope to meet. He was a perfect, sweet, gentle boy.”

The court heard that Hakeem was a wanted man after a feud in his gang over more than £45,000 robbed from security guards outside banks in January and February last year. When rumours circulated that some of the proceeds were not being shared, Javarie Crighton, 21, a gang member, confronted the leader, Orando Madden, and was stabbed to death. Hakeem was accused of holding the missing money and Sannoh, a friend of Crighton, wanted revenge.

Terrified, Madden had turned himself in to police and Hakeem “was the only available target for revenge”, the jury was told.

Sannoh and Noor, a drug dealer from the Pelican Crew gang, burst in to the Dosunmus’ family home in Peckham, southeast London, at around 12.45am on February 6 last year. Michael’s sister, Shakira, who heard the gunfire from her bedroom, was confronted by one of the killers as they fled before she found her brother.

After the murder Noor fled to Ipswich and drunkenly confessed to a fellow Somali, the court heard.

Hakeem was jailed for two years in April for his part in the security van robberies. The judge reduced the sentence after hearing that he blamed himself for Michael’s death.

Detective Superintendent Gary Richardson said: “The murder was carried out in the manner of a cold-blooded execution; the victim was an innocent boy. We pay tribute to Michael’s family who have reacted with great dignity and those members of the community in Peckham who have come forward and shown they are not prepared to see our streets taken over by people of violence.”

Times Recommends

• What makes the perfect mum?
• To keep me stress-free, no more awareness days, please
• What do lottery winners buy?