Police are asking any witnesses, or anyone who may have information about the attack on the 13-year-old girl to contact them. The victim was raped at around 9pm on Saturday, 30 November.
Anyone with information is asked to call Crimestoppers anonymously on 0800 555 111.
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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.