Police are seeking a second man in relation to a car crash that killed three teenage pedestrians in west London on Friday night.
A 28-year-old man has been arrested on suspicion of dangerous driving after a black Audi, believed to be travelling at speed, mounted the pavement on Shepiston Lane, Hayes.
It is understood the three victims, named locally only as George, Harry and Josh, had been on their way to a birthday party at a nearby football club with friends when they were killed.
The suspect was being questioned at a north London police station on Saturday night.
Now the Met have said they believe at least one other male travelling in the Audi fled the scene.
The second male has yet to be apprehended and investigators have not ruled out more passengers being in the car.
The Met said in a statement: "Enquiries are ongoing to establish the full circumstances of the collision and the number of occupants in the vehicle involved."
Emergency services were called at 8.41pm on Friday, but despite the efforts of paramedics, all three victims were pronounced dead at the scene.
Two were aged 16 and one was 17.
Staff at the nearby Esso garage said a group of teenagers had been fighting near the entrance to the forecourt at about 8.40pm.
One cashier said the police had come to inspect CCTV footage of the brawl, but said he did not know if it was related to the crash.
Schools administrator Jake Webb, 18, saw two white youths attacking an Asian man on the side of the road near the scene as he was driving towards Hayes.
He said the Asian man seemed heavily intoxicated, adding: "We saw two white boys and they were attacking an Asian man. They were just kicking and punching him."
He and his friend, Amamdeep Matharoo, 27, were so concerned about the assault they pulled over.
Mr Webb said: "I said 'can you stop that, we're going to call 999'.
"They said 'please call the police. He's hit our friend'."
He continued: "The Asian man - he looked like he was intoxicated, he couldn't even walk in a straight line."
When asked if the Asian man's unstable appearance could have been as a result of being attacked, he replied: "He couldn't walk in a straight line and they weren't attacking him enough to cause injury like that."
Both Mr Webb and Mr Matharoo returned to the scene on Saturday morning to lay tributes to the victims.
Mr Matharoo said: "The lads were shouting on the phone. They were saying 'three of our friends are dead'. They were hysterical and in pieces."
One tribute left at the scene read: "George Boy, I love you so much, love Kev, Vinnie."
Another said: "I thought I would never have to write this and I don't know what to write but I will always love and miss you millions."
Elsewhere, a card read "To my bro, always together forever," while a fourth said: "To my darling baby boi my heart is broken, love mum, Vinnie."
Tony Kitchin, 44, who works as a security guard at a haulage firm nearby, said: "This road is busy 24/7. It's a speed trap.
"I'm really surprised we haven't had more horrific accidents like this."
He added: "No parent should have to deal with that. My heartfelt sympathies go out to the family and friends of the people who lost their lives last night."
Detective Superintendent Jane Shaw, of the Met's Serious Collision Investigation Unit, said: "These are horrific circumstances that have resulted in three young people on a night out losing their lives."
She added: "We know that there was a large party nearby and many people would have been travelling through the area and saw what happened or witnessed the aftermath.
"I need these witnesses to contact police immediately.
"We are also particularly keen to trace other motorists travelling through the area at the time."