Detectives investigating the murder of a seven-year-old boy, Joel Urhie, are investigating whether the arson attack is linked to a local gang dispute.

The child was found dead after the blaze in Deptford, south east London, on Tuesday. His mother, Sophie, and his 19-year-old sister escaped by jumping out of a first-floor window.

They were taken to hospital with non-life threatening injuries.

Sources said one line of inquiry was that the attack was gang-related amid reports that the boy’s older brother, Sam, aged 21, may have been the target.

But Detective Superintendent Jane Corrigan said the exact motive was still not known. She told reporters at a press conference on Tuesday evening that it was not believed Joel was the target of the attack.

“It is difficult to imagine a seven-year-old is the motive for the attack, especially at 3am,” she said.

Appealing for information, she added: “An innocent seven-year-old boy has lost his life in what should have been the safest place for him, his home. We’re treating this as a murder investigation,” she said. 

“We believe that the fire was started deliberately but at this stage I am unable to go into any further detail due to operational reasons.”

She continued: “We have no idea what the motive for this attack was. We’ve got no suspects at this time.”

Alex Hope, 29, said he knew Joel’s brother Sam when they were growing up. Responding to reports Sam may have been the intended target, he said: “That would really surprise me if that’s the case. I haven’t seen him in a long time but growing up he was a lovely kid.” 

Family friend Grace Gbenedio, 56, has been visiting the family in hospital. When asked about speculation that Sam could have been the target, she replied: “It can’t be possible.” 

Peter Hill, 69, who lives on the fourth floor in a neighbouring block of flats said he heard an “aggrieved bloke shouting his head off” in the early hours of the morning before the fire.

“I was lying in bed just next to the window, that’s how I heard the noise,” he said.

“I heard a male, a grown-up black male, shouting his head off.”

He added: “He seemed aggrieved, he seemed unhappy, he seemed pissed off. That’s the impression I got.”

Speaking to reporters outside the house he moved out of around five years ago, Joel’s father John Urhie, 54, said: “He was a very lovely boy who was just loving life and it’s a terrible loss.”

He said he was supposed to see his son on Monday but did not because the boy’s mother wanted to take him out. Describing his son, Mr Urhie said: “He played with everyone around here. He was a very nice looking boy.

“It’s terrible, the pain we can never forget.”

CCTV footage from a camera system above a flat on the other side from Joel’s family home has been seized by detectives. The camera does not point at the Uhrie house, but may have captured the person or people who started the blaze as they arrived at or left the scene. 

Six fire engines and around 35 firefighters tackled the blaze in Adolphus Street after they were called at 3.25am on Tuesday.

Nearby properties were evacuated as a precaution and crews brought the fire under control just before 4.50am.

Gbenedio said she rushed outside after hearing screams.

She said she held Mrs Urhie and asked her where Joel was, and she said: “My son is inside, my son is inside.”

Mrs Gbenedio said: “She was on the floor crying ‘Help, help, help’.”