A 26-year-old found stabbed to death after a car crash in west London was one of three young men killed during a weekend of knife violence across the capital.
A 27-year-old man was knifed to death at a house party, while a third man, 24, died after he was stabbed during a fight in separate incidents in different areas of east London.
Murder detectives believe the 26-year-old was wounded in an altercation 100 metres away from West Ealing railway station before crashing his car and are not treating the incident as a "road rage" attack.
Ruth Holmstock, 72, whose flat overlooks the scene of the crash, said she heard a single "thump".
"It was one of those 'oh f***' sort of crunches," she said. "The sort of noise you make when you reverse into a gate, but it was loud enough to make me go and see what it was.
"There were a lot of people hanging around. It looked like any other crash, like they were swapping insurance details."
Police were called shortly before 1.20am on Sunday and the victim was pronounced dead at the scene after he was found in a car suffering from a stab wound.
A picture of the scene appeared to show a saloon car which had been hit by a Mini positioned sideways across Drayton Green Road.
Detective Chief Inspector Neil John said: "We believe the victim was involved in an altercation 100 metres from the railway station on The Avenue.
"This is a busy street with a number of shops and restaurants and if anybody was in the area and saw something, no matter how small, I would urge them to contact police."
Ms Holmstock said she saw five police cars, along with an ambulance and other medics' vehicles.
She said there was no sign of any injuries at first and police had removed someone from the car.
"I would never have dreamt that there was anyone injured," she continued. There was nothing to see. I was really surprised when the police got here.
"One minute the road was empty and the next minute they were doing CPR on someone."
Kiran Ramachandraiah, who lives in the same block of flats, said he woke up at about 2am to see medics trying to revive the victim.
"I couldn't see the person," he said. "He was completely surrounded by police and paramedics."
The victim has not been formally identified, but Scotland Yard said his family have been told.
No arrests have been made and a post-mortem examination has not yet been carried out to determine the cause of death.
Seven men have been arrested on suspicion of murder and attempted murder over the death of the 27-year-old, who was knifed to death at a house party in Whitechapel, east London, on Saturday morning.
Three other people were also stabbed, but their injuries are not life-threatening.
There have been no arrests over the death of the 24-year-old, who died in hospital on Sunday afternoon, after he was found in Ilford.
Police had been called to reports of a group fighting in Redbridge and another man in his 20s was taken to hospital with non-life-threatening injuries believed to be linked to the incident.