Police have released an image of Mohammed Hussein as they continue to hunt for his killer.
A post-mortem at Haringey Mortuary gave his cause of death as a single shotgun would to his chest.
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Officers were given the touching letter at Brixton Station while they were on a reassurance patrol after yesterday's attack
The 52-year-old had previous convictions for violence but was not on the anti-terror watchlist.
In a statement Charlton Athletic said: Keith was a true hero who will be greatly missed by all the Charlton family and everyone at the club.