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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Metropolitan Police officer, Tom Harrison, has been crawling the course since the race began on Sunday morning.
The Old Bailey heard how Syed tried to get weapons online, including a bomb vest, and trawled the web to find a busy area launch an attack.
Hours after completing Sunday's course some of the runners put their medals on auction site eBay, with one attracting bids of almost £92.