Police have obtained CCTV footage that may contain clues to the suspected arson attack in which a seven-year-old boy died.

A murder inquiry was launched after Joel Urhie died in a blaze in Deptford, south-east London, early on Tuesday morning. Police said it was not yet known what the motive for the attack was or who was the intended target.

Detectives now have footage from a flat across the road from Joel’s family home. The flat’s occupant, Tien Thuan Nguyen, 56, said police had taken the footage, which he said he had not watched.

The camera, at the rear of the flat, does not point at the Urhie house but may have captured the person or people who started the blaze as they arrived at or left the scene.

Detectives from Scotland Yard’s homicide and major crime command took over the investigation on Tuesday afternoon. They are usually cautious about settling on a possible motive too early and thus potentially ruling out other lines of inquiry.

Joel’s mother and another woman were inside the house when the fire took hold and managed to escape by jumping out of a first-floor window. The flames were so fierce that Joel could not be rescued.

The two women were taken to Lewisham hospital with non-life-threatening injuries.

Grace Gbenedio, 56, a family friend, said she had visited them in hospital on Tuesday. “They are doing well,” she said. She had also spoken to Joel’s 21-year-old brother, Sam, to ask how he was feeling and he had said he was “fine as much as possible”.

Asked about speculation that Sam could have been the target, Gbenedio said: “It can’t be possible. I don’t think anyone would be thinking he’s a target. It’s a shame people are thinking like that.”

A local man who asked not to be named was also surprised by suggestions that Joel’s brother could have been targeted. “He’s a good guy. He just looks like an average person who helps out his mum and I literally hear nothing bad,” he said.

Friends and neighbours said Joel was a friendly and popular boy who went to church with his mother.

His father, John Urhie, who moved out of the family home five years ago, told reporters at the scene on Tuesday: “When I came, the first thing I saw was my daughter inside the ambulance. They said Joel’s dead, and there’s nothing I can do about it. He was a very lovely boy who was just loving life, and it’s a terrible loss.”

A spokeswoman for Joel’s school, the Tidemill Academy, which is a short walk from his home, said: “We were deeply saddened to hear the tragic news about Joel Urhie, one of our Year 2 pupils.

“Joel was a much-loved member of our school community. He was a friendly, fun and smiley boy who loved to make people laugh.

“He enjoyed sport and reading. Our thoughts and prayers are with his family at this extremely difficult time.”