CCTV footage has been released following a serious assault in Cricklewood in August 2016.
Police were called to an assault on Oaklands Passage in Cricklewood in Brent on August 2, at just before 5.30pm.
Officers gave first aid to a 19-year-old man who had been assaulted by three men, one of whom repeatedly used a hammer, before another assaulted the man with a glass bottle.
The teenager suffered a fractured skull and continues to have seizures as a result of his injuries.
The CCTV footage shows three suspects walk into the alley at around 5.20pm, before fleeing towards Cricklewood Broadway.
After approaching the victim in the alleyway, one suspect punched the victim in the face, whilst the other two kicked and punched him to the floor in what police are describing as an "unprovoked and vicious attack", leaving the suspect bleeding on the floor.
The London Ambulance Service took the victim to a central London hospital for treatment.
One of the suspects is described as an Asian man wearing a black jacket, black tracksuit trousers with "Adidas" written down the side and black trainers with white soles. He was carrying a blue bag.
The second suspect was wearing a grey tracksuit and trainers and is described as an Asian man.
The third suspect is described as a tall Asian man who was wearing a black jacket, grey tracksuit bottoms with a white stripe down the side and black trainers.
"This is a shocking incident that has left the victim with life changing injuries," said detective constable Rupy Ghatrora, from Brent CID.
"We are keen to identify the three men in the CCTV footage so we can speak to them about the incident.
"We would also urge anyone who witnessed the incident to contact us."
Police are urging anyone with information to call them on 101 or to get in touch by tweeting @MetCC, alternatively, you can call Crimestoppers anonymously on 0800 555 111.
No arrests have been made and enquiries into the incident continue.
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