Ten males aged from their teens to early 20s have been arrested after a teenager was knifed to death in a north London park, Scotland Yard said.
Police are appealing for information after officers were called at 5.54pm on Bank Holiday Monday to Montrose Park, Edgware, following reports of a group of males fighting.
An 18-year-old male was found suffering from a stab injury in a tennis court area of the park.
He was treated by London's Air Ambulance and London Ambulance Service at the scene but despite the best efforts of paramedics, he was pronounced dead at 7.19pm.
A post-mortem examination is expected to be held on Thursday and while officers believe they know the identity of the deceased, efforts to inform his next of kin continue.
On Tuesday, the Metropolitan Police said 10 males have been arrested in connection with the incident on suspicion of offences including affray and murder, and remain in police custody.
Detective Chief Inspector Claire Hine said: "We know the park was busy with people enjoying the sunshine on the bank holiday when this horrific incident unfolded.
"We have spoken to a number of people who have told us what they saw, and we remain keen to hear from anyone who has information, video or images that could assist us.
"A young man has lost his life in violent circumstances and it is imperative that we have a full understanding of the chain of events that has led up to it."
Detective Superintendent Barry Loader, from the North West Command Unit, added: "Residents can expect to see an enhanced police presence in the area following this incident.
"Our thoughts of course are with the young man who has lost his life and we are supporting our colleagues as they work to investigate the circumstances around this terrible incident."
Any witnesses or those with information, video or images that could assist officers are asked to call 101 reference CAD 5436/31 May.