A teenager killed in Thornton Heath last Friday was stabbed in the heart, it was revealed today.

At the opening of the inquest into the death of Dwaine Douglas, Detective Chief Inspective Phillip Adams told Croydon Coroner's Court that, according to initial postmortem examination reports, the 18-year-old died from a haemorrhage.

The officer leading the murder inquiry added that Mr Douglas had been travelling with friends from Streatham to Croydon when they had "reason to stop in Thornton Heath where they got into an altercation".

Mr Douglas, who lived in Tulse Hill, was stabbed near Tesco, on the corner of Parchmore and Brigstock Road, at around 10pm and then driven to Mayday Hospital by two friends.

A 16-year-old who was also treated at the hospital for a slash wound to his arm is believed to have made his way to hospital separately.

Mr Douglas died an hour after arriving at hospital.

D Chief Insp Adams said a weapon has not yet been found and police are continuing to search the area around Parchmore Road, Bulganak Road and Kettering Court as well as the front of the Tesco store.

One line of inquiry police are said to be looking into is the possibility that Dwaine was involved in a robbery when he was stabbed.

The possibility the incident was gang related has been dismissed by police.

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 on Tuesday. Two 16-year-olds and another 19-year-old were also arrested but later bailed.

D Ch Insp Adams said he was "confident" about the latest arrest and said the investigation team had had "some luck" with CCTV images from the night.

"The area was busy and this all happened very quickly," he said. "Many people in the area were probably not aware this happened apart from seeing a group of youths walking quickly away."

He said the attack is "likely to have happened" out of the sight of the public.

Detectives want to speak to anyone who saw three or four youths, one of whom may have been staggering, running across the front of the Tesco store from the direction of Thornton Heath station before getting into a car in Parchmore Road.

An anniversary appeal is due to be held in the area this Friday between 9.30pm and 11.30pm.

Mr Douglas' uncle attended the hearing at Croydon Coroner's Court and his family are said to be "extremely shocked and saddened".

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