A 34-year-old man was stabbed to death after intervening in a fight at an illegal rave in south London.
Sean Williams was stabbed in the neck in the early hours of Sunday morning after attending an unlicensed music event at Culverley Road in Catford, the Metropolitan Police said.
Police and the London Ambulance Service were called to the nearby Thornsbeach Road to reports of a stabbing, and Mr Williams died at the scene shortly after 6.15am.
Detective Chief Inspector Kate Kieran, who is leading the murder investigation, said: “At this early stage we believe that both the victim and the suspect had attended an unlicensed music event at Culverley Road, SE6, during which a fight broke out between two men.
“The victim intervened in this fight and suffered a fatal injury.
“I know there were around 100 people at the event and someone who was there knows the identity of the person responsible.
“I want these people to do the right thing and get in touch.
“I also urge the person responsible to hand themselves into police.”
No arrests have been made, the Met said.
A second victim, 37, took himself to a south London hospital with a non-life-threatening knife injury to his hand, police added.