London's top police officer, Commissioner Bernard Hogan-Howe, gave a lesson on the dangers of knife crime to teenagers at Edmonton County School - including the friends of a pupil who was killed last year.
More top news
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.