A 19-year-old man is in a critical condition in hospital after being stabbed in New Cross.
Police say it happened on New Cross Road, near the junction with Clifton Rise, at around 3:30am.
Police say it is not connected to the earlier stabbing of a 14-year-old boy in Lee.
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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.