After his elder brother's murder, Amine set up a association called Conscience, which aims to help young people in Marseille's poor estates to escape the clutches of powerful drugs gangs.
He was a high-school student at the time, and then last year ran unsuccessfully for the Green Party in European and legislative elections. He recently wrote a book called Marseille Wipe your Tears – Life and Death in a Land of Drugs and now, aged 22, he lives under police protection after receiving death threats.
"It's just so sad for my friend and for his mother," said Christine Juste, a Green Party city councillor in Marseille.
"No mother should go through that — losing two children. And I'm so angry that in France's second city, people can be murdered so easily in plain daylight."
Vendettas spawn successions of revenge murders, with killers sometimes as young as 15. So far there have been 14 drugs-related murders this year.
Amine Kessaci's association, Conscience, has branches in several other towns and cities. Its main activities involve providing help and advice to families who have lost sons in drugs violence, and creating links between ex-delinquents and employers.
When he was 17, Amine was selected to meet Emmanuel Macron when the president came to Marseille in 2021 to discuss projects to improve life in the city.
A local newspaper dubbed him in its headline: "The kid from the estates who has Macron's ear."
Explaining his decision to run for election the young campaigner wrote in his book: "Politics never held out its hand to me, so I decided to grab it by the throat. Brahim – it was you who threw me into politics the day you burned in a car."