The 16 year-old, who cannot be named for legal reasons, stabbed him to death on 20 December last year, the Old Bailey heard.
He attacked Jamaly, also 16, before fleeing the scene in Seward Street. Paramedics battled to save the schoolboy’s life but his injuries were too severe.
The killer was then arrested after arriving into the UK at Gatwick Airport nine days later.
A murder investigation was launched led by Detective Chief Inspector Kate Kieran who tracked down the suspect.
He said after the conviction: “While nothing can bring Jamaly back, I am pleased that the guilty plea will save his family having to endure a murder trial that would have been extremely painful for them.
“My thoughts are with them today.”
The killer was remanded in custody until sentencing at the Old Bailey on November 17.