A man stabbed to death in Thornton Heath could have been knifed while trying to mug somebody.

The possibility Dwaine Douglas was attacked after trying to rob somebody is one line of inquiry detectives are investigating.

The 18-year-old was stabbed during a fight in Parchmore Road on Friday night (May 18).

The Tulse Hill teenager died an hour after admitting himself to Mayday Hospital at 10.30pm.

He was accompanied by a 16-year-old friend who was treated for a slash wound to his arm and later discharged, along with two others.

The stabbing was believed to have taken place during a fight involving a number of men near the Tesco car park at about 10pm. Friends are thought to have taken Mr Douglas to hospital.

Four men have been arrested in connection with the stabbing. A 23-year-old man from Thornton Heath was being questioned by detectives at a south London police station yesterday. Two 16-year-olds and another 19-year-old were also arrested but later bailed.

Initial reports suggested the incident was the latest in a long line of gang-related deaths which have blighted south London. But police said Mr Douglas was not connected to any gang.

Thornton Heath teenager Eugene Attram, who attended the same school as Dwaine - Ernest Bevin in Tooting - was stabbed to death during a vicious street brawl involving around 30 youths in November last year.

Mr Douglas, known as Flea, had two younger brothers and a sister. James Smartt-Ford, the 16-year-old gunned down in Streatham Ice Rink in February, was said to be a friend.

His death came a year after 17-year-old Gavin Brown from South Norwood was stabbed in the neck at Shirley's Parkfields Recreation Ground.

Borough commander Mark Gore said there was no evidence to suggest the incident was gang-related.

Speaking at the launch of Croydon's new crime reduction strategy, Chief Superintendent Gore added: "There are many lines we are exploring, including the gang aspect, although there is still nothing clear on whether there were any gang connections.

"The bottom line is, this is the tragic death of a young black male who has died as the result of someone else's actions."

A postmortem examination held at Thornton Heath mortuary on Saturday gave Mr Douglas' cause of death as a stab wound.

A number of recycling bins in Parchmore Road were cordoned off by police before being searched.

Detective Chief Inspector Phil Adams, who is leading the investigation, said: "We are appealing for anyone who may have witnessed the fight or anyone who has any information to call police.

"We are not linking this murder with any other recent murders in south London. I am keeping an open mind as to the motive for the killing but I do not believe it to be related to inter-gang rivalry."

A dispersal order - which covers the Parchmore Road area - remains in place until August 19.

Anyone who witnessed the incident should contact the incident room at Lewisham on 020 8721 4868 or Crimestoppers on 0800 555 111.