The CCTV footage, published by Met Police , was captured after the brutal attack took place outside Capital City Academy, in Doyle Gardens, on January 23, 2017.
The video shows a youth dressed in dark clothes running away from the school gates, where the stabbing took place as children left school.
On Wednesday (September 6), a 15-year-old boy, who cannot be identified for legal reasons, was jailed for the attack on Quamari.
Throughout the murder trial, the court heard that the knife-wielding teenager wore a mask and waited for his victim outside the school gates.
As children left the school, the teenager saw “happy and hardworking” GCSE student Quamari and chased him with a large kitchen knife.
After the victim ran for his life, shouting for help and desperately saying he was going to be stabbed, the defendant caught up with him and stabbed him three times.
The young Quamari was taken to hospital, where he managed to tell a nurse who had carried out the attack before he died from his injuries .
Despite wearing a mask, witnesses of the stabbing recognised the killer and he was arrested the next day, January 24.
Quamari's mother, Lillian Serunkuma, described the killer's acts as “pure evil” in a statement read out in court .
"You never gave Quamari a second chance to defend himself,” she wrote.
"You took his life in a cold and malicious way."
The court also heard the defendant had a string of convictions, including one for punching a girl.
In a statement expressing remorse, the 15-year-old defendant said: "I want to say that I'm sorry for what I did.
"I don't know why I did it. I was scared and confused.
"I'm telling the truth for Quamari's mum and dad. I'm sorry. I didn't mean Quamari to get so hurt.
"I'm not a murderer. I'm not a waste man. I didn't want him to die. I want to have a different life but I don't know how. I'm trying."
After sentencing the youth to 14 years in prison, Judge John Bevan QC said: “This is a bad case of its kind because Quamari can have done nothing to merit an attack of this severity.
"His death was a product of a total lack of self-control combined with the cowardice of knifing an unarmed victim."
Judge Bevan also said it was “infinitely depressing" to sentence a young person for such a serious crime.
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