CCTV images released today show the moment before an innocent teenager is murdered, because his killers mistakenly thought he was a member of a rival gang.
Kwame Ofosu-Asare wasn't.
But he was stabbed to death on a housing estate in Brixton.
Today his killers were jailed for life.
Some of you may be upset by some of the images in this report by Piers Hopkirk.
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"All it takes is for somebody to see me - and I could just die, just like that. I could want to go to the shop and not come home."
Before the killing, Peters searched the internet for "serial killers", "treatment of child killers in prison" and "premeditated murder".
Arriva Rail North, Greater Anglia and South Western Railway are all affected.