Two teenagers have been locked up for life for the "callous, casual and irresponsible" murder of Jodie Chesney.
Drug dealer Svenson Ong-a-Kwie, 19, and his 17-year-old runner Arron Isaacs had been looking to take revenge on rivals when they killed Jodie by mistake, the Old Bailey heard.
The 17-year-old student had been relaxing with friends in Amy's Park in Harold Hill, east London, on the evening of March 1 when two figures emerged from the dark and one stabbed her in the back.
She screamed and collapsed in the arms of her boyfriend, Eddie Coyle, 18, as her attackers made off in a fellow drug dealer's car.
Days later, they were arrested together as they fled from the rear of a house connected with the youth.
The defendants denied Jodie's murder, each blaming the other for inflicting the fatal wound.
But prosecutor Crispin Aylett QC told jurors that both were responsible for the killing, amid incidents of "casual violence" in the drug-dealing world. The jury deliberated for less than six hours to find them guilty last week of Jodie's murder.
Police body cam footage of the moment Ong-a-Kwie and Isaacs were arrested
Judge Wendy Joseph QC handed Ong-a-Kwie a life sentence with a minimum of 26 years.
She sentenced Isaacs to be detained at Her Majesty's Pleasure for at least 18 years.
She said that Jodie's death led to a "world of anguish" for her family, which came amid "tit for tat" incidents.
Jodie was the victim of "callous, casual and irresponsible violence" which had shocked the community "to the core", she said.
On the evidence, she found Ong-a-Kwie was the stabber and Isaacs his "enthusiastic supporter".
The judge lamented the impact of criminals that had "carved up areas of the capital of this country".
She added: "The dangers this brings to decent law-abiding members of the public is graphically spelled out in this case."
The court heard moving tributes to Jodie and the "ripple effect" her murder had among friends, family and the wider community.
Mr Coyle has been left with post-traumatic stress from witnessing her murder.
He said: "Jodie was funny, silly, she always made fun of me and she had a bright future ahead of her. She was full of energy and was always out doing something. We had been going out for three months.
"I've never lost anyone before and for the first funeral I've gone to to be my own girlfriend's is incredibly hard. I loved her."
Jodie's father, Peter Chesney, who gave up a job in the City, said: "I have lost the most precious human being I will ever know. I have no idea how I'm going to continue my life or come to terms with the loss."
Her sister, Lucy, said: "Jodie will be greatly missed and the people who caused such tragedy to a whole family should hang their head in shame. You have ripped away a bright future that was destined to make a change to many lives."
The court heard that Ong-a-Kwie had convictions for possessing and supplying drugs.
He admitted being in breach of a six-week suspended sentence for handling stolen jewellery dating back to October last year.
The 17-year-old defendant had previous convictions for possessing a screwdriver, actual bodily harm, possession of cannabis as well as aggravated vehicle-taking.