Two men were stabbed to death after a gang of up to 15 people laid siege to their van in south-west London.
Police found the victims, both Asian men aged 23 and 24, fatally wounded outside a house in Fircroft Road, Tooting. Both later died in hospital.
A gang of Asian men smashed the white van's windows, before the two men were either dragged from it, or climbed out. They were then stabbed outside the van.
Four men have been arrested in connection with the deaths.
A third man, who was in the driver's seat of the van was unharmed.
The gang attacked the men at the junction of Fircroft Road and Tooting High Street at about 0016 BST on Saturday.
Det Ch Insp Mick Duthie said: "At this early stage of the investigation we are keeping an open mind as to why one group of Asian men attacked another.
"This attack resulted in the tragic death of two young men."
He said police want to speak to any other people who may have been involved.
Roads surrounding Upper Tooting Road were sealed off as officers carried out forensic examinations.