Kareem, 20, was gunned down on Askew Road, Shepherd’s Bush, shortly after 12.30am on 8 June as he left a convenience store and rode a scooter to a friend’s house.
In the early hours of Tuesday, investigators from the Metropolitan Police arrested five men aged between 18 and 24, a 16-year-old boy and a 35-year-old woman on suspicion of murder.
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Detective chief inspector Wayne Jolley, who is on the specialist crime team and who leads the investigation, said: “This is a significant development in the investigation, however we will not be complacent. We will continue to work hard to make sure those responsible are brought to justice.
“I believe this murder to have been a case of mistaken identity, perpetrated recklessly and with no regard whatsoever for human life.
“Alexander’s death is a tragic reminder that carrying a gun has devastating consequences, I urge anyone with information to come forward and speak with us.”
Investigators have scoured CCTV to trace the route taken by a white Range Rover thought to be linked to the shooting that was found burnt out 25 minutes after the police were called.
All seven of those arrested were taken into custody at London police stations, Met Police said.
They include a 16-year-old boy and three men, aged 18, 20 and 23, all from Ealing, west London, a 24-year-old man from Brent, in north-west London, and a 20-year-old man and 35-year-old woman, both from Hounslow, west London.
At Kareem’s funeral on 29 July, his sister Khafi Kareem, 30, urged the public not to dismiss her brother as “just another black boy who’s been shot”.
She told the PA news agency: “To anybody who’s seen this (in the news) and is thinking this is just another black boy who’s been shot by violence, I want to tell you that is not the case.
“Alex’s life mattered, he had a future ahead of him, he’s not just another black boy.
“He had a family, he had friends, this is real.”
Additional reporting by PA