Officers have said that they believe two violent incidents in Twickenham, including the death of a man in his 20s and 16-year-old found slashed, to be linked.
Police were called to Alexander Close on January 8 after reports of a stabbing at 11.56pm.
London Ambulance Service also attended and found a 16-year-old boy with a slash to his leg.
He was taken to hospital where his condition was found not to be life-threatening.
Around the same time, British Transport Police (BTP) were called to the Strawberry Hill railway station on January 8 and found a man in his 20s seriously injured.
London Ambulance Service and the Metropolitan Police also attended but the victim was pronounced dead at the scene.
His injuries were described as serious and “consistent with being stabbed”.
Four men have since been arrested and remain in custody – including the 16-year-old who was injured in Alexander Close.
Police are now treating the two incidents as related.
Anyone with further information that can help police should call 101 and request to submit a report via British Transport Police with reference to 630/ 8 Jan - re Strawberry Hill and 7168/ 8 Jan - re Alexander Close.
Detective Chief Inspector Sam Blackburn said: “This is a senseless act of violence which has seen the tragic death of a young man.
“This investigation remains in the early stages and the station will remain closed while we continue our enquiries.
“I urge anyone with information that may help us piece together the moments leading up to this to contact BTP by texting 61016 or calling 0800 40 50 40 quoting reference 630 of 08/01/24. Alternatively, you can call Crimestoppers anonymously on 0800 555 111."
Trains are currently not calling at the station due to an ongoing investigation which is expected to continue throughout the day.
Southwestern Railway, which tweeted shortly after midnight: "The police dealing with an incident is affecting the railway at Strawberry Hill.
"Trains may be cancelled, delayed or revised because of this problem."
In a recent update, they added: "We have now received an update and disruption to our services is now expected until the end of the day."
A spokesperson for British Transport Police said: “Detectives at British Transport Police (BTP) have launched a murder investigation after a man sadly died at Strawberry Hill railway station last night.
“Officers were called to the station at 11.53pm on 8 January following reports of an injured man.
“Officers attended alongside colleagues from the Metropolitan Police and London Ambulance Service and a man was found with a serious injury, consistent with being stabbed.
“Despite their best efforts, a man in his 20s was sadly pronounced dead at the scene.
“Four men have been arrested in connection and remain in police custody this morning.”
A spokesperson for the Metropolitan Police said: “Police were called at 23:56hrs on Monday, 8 January to a stabbing in Alexander Close, Twickenham.
“Officers responded with LAS paramedics.
“A 16-year-old boy was found with a laceration to his leg. His condition is not being treated as life-threatening.
“A short time earlier police had been alerted to a stabbing at Strawberry Hill BR Station. A man in his 20s was found injured and was pronounced dead at the scene.
“At this time the incidents are being treated as linked.
“British Transport Police will investigate the murder. Officers from the Met will support.
“Four males have been arrested. The male injured in Alexander Close is among those arrested.
“Anyone with information that can help police should call 101 ref BTP ref 630/ 8 Jan - re Strawberry Hill and 7168/ 8 Jan - re Alexander Close.”
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