Police are looking into possible links with another stabbing in South London on Friday. The incident happened around lunchtime in West Norwood. A 17 year old was injured and is in a stable condition in hospital.
One man has been arrested over this attack, and continues to be questioned by police.
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Peter Barnett made hundreds of trips from his home in Oxfordshire to Marylebone station without paying the full fare.
Police say he may have attacked more children and urged them to come forward.
The suspect walked up to a Tesco employee and shoulder barged him to the ground before punching him repeatedly in the face.