Police are appealing for videos and pictures after a 28-year-old man died in a shooting during a gathering of up to 100 people.
Officers were called to Cheney Row Park in Waltham Forest shortly after midnight last night.
Soon afterwards, two men turned up at an east London hospital – one of them later died of gunshot wounds.
The other man, believed to be in his 30s, had suffered stab wounds. He has since been discharged from hospital and arrested in connection with the incident.
Det Chief Inspector Kelly Allen from the Metropolitan Police said: “My heart goes out to the family of the man who has lost his life in this reckless act of violence.
“I believe there were 50 to 100 people gathered in and around Cheney Row Park at the time of the shooting with music playing.
“I urgently need to speak with everyone who was at that event – even if you do not believe you saw anything significant, you need to come forward.
“There will have been footage and images captured at the event, and we need to see these.
“Please ensure that all such material is saved – we will provide a link for it to be uploaded shortly.
“To anyone considering whether or not to come forward to police, I ask you to put yourself in the position of the victim’s grieving mother and father this morning. They deserve answers.”
Anyone with information is asked contact police on 101, quoting reference 267/24jul – or call Crimestoppers anonymously on 0800 555 111.