A 25-year-old-man has been released on police bail in connection with a motorway crash which left two people dead and another six injured.
The man, from east London, was arrested on suspicion of causing death by dangerous driving after a crash involving two BMWs on the M1 near Watford in Hertfordshire.
The driver and rear seat passengers of one of the cars were killed in the crash, which happened shortly before 2.40am on Monday.
The two men have not been named by police but were aged 22 and 24 and both from east London. Six other people were taken to hospital for treatment following the crash.
Witnesses have said the two cars "appeared to be having a high-speed race".
Basit Nasir told the Evening Standard that the BMWs had sped past him at around 140mph. He said: "It was total mayhem. There was mangled metal everywhere. It was foolish of them to drive at this sort of speed. It was raining as well."
Mr Nasir said that four men in a Mercedes arrived at the crash scene and scuffled with survivors.
He told the newspaper: "They all jumped out and everybody started punching each other. They said, 'What have you done? You have killed them'. I tried to break up the fight and called the police from my mobile."
The accident, which happened between junctions five and four, resulted in the closure of five junctions of the motorway in both directions, and the south-bound stretch was shut for several hours.
The 25-year-old man has been released on police bail pending further inquiries, a Hertfordshire Police spokeswoman said. The force has appealed for witnesses to the collision or the events leading up to it to contact them on 101.