A thug who knocked a teenage girl out in a random attack had followed her from her house before striking minutes later, police have said.
Shocking CCTV footage of the man jogging up behind the 16-year-old and smacking her around the head has been released as detectives try to trace the violent culprit.
Detective Constable Glenn Peach said: "As you can see from the footage, she is completely unaware of what's going on. She says that there was a strange guy looking at her as she left her house. There's other footage and she's walking along normally and he's following about 30 seconds behind.
"It's one of the most shocking things I've seen because of its randomness. At this time there's nothing to suggest she knew him or that there is any history between her and this person. It appears to be a random attack."
The girl was left unconscious and sprawled across the pavement as her attacker casually jogged off. She is now recovering after the attack which happened outside the Black Lion pub in High Street, Plaistow, east London, at around 12.30pm on November 13.
Mr Peach said: "She is in shock and in pain and has had some work done on her teeth, but she is bearing up really well considering what has happened."
The girl told ITV's London Tonight: "I hope he does get caught so he doesn't do it again to another person. I hope I'm his last victim."
Police are appealing for witnesses or anyone who knows the man to come forward.
The attacker was a black, muscular man, aged between 25 and 30, who was wearing a black baseball jacket and jeans. He was 6ft and had a shaved head. He ran off in the direction of Green Gate Street after the attack.
Anyone with information can contact Newham Violent Crime Unit on 020 8217 5890 or Crimestoppers on 0800 555 111.