Tilisha Goupall tends a memorial to her younger brother, Jermaine Goupall, at the location where he was stabbed to death in south London in August 2017.

Knives and gangs: What's driving Britain's broken boys to crime?

Story by Zahid Mahmood; Photos by Sarah Tilotta, for CNN

Updated 11:54 AM ET, Sat December 15, 2018