Teenagers could hold the key to catching those responsible for an arson attack that led to the death of a teenage girl, police said today.

Maleha Masud, 15, died at 9pm last night, four days after the attack on her Lessingham Avenue home.

Her three siblings are all still in a critical condition in hospital, suffering from serious smoke inhalation problems and burns.

DCI Damian Allain, of the Met Police’s homicide and serious crime command, said the youth community held vital clues.

He said: “We have good intelligence that people in the Tooting community know who did this.

“This was a cowardly act. People may know who did this but have a question of loyalties. “She [Maleha] was a good looking girl with her whole life in front of her she has now died so people should call us, even anonymously if they want to.”

Maleha’s schoolfriends from the all-girl Burntwood School, Tooting, left flowers at the fire-ravaged house this afternoon.

One of them said: “Maleha was a lovely girl . . . she died for no reason. We want someone to come forward. So many people are hurt, everyone loved her.”

D Chief Insp Allain said he was “keeping an open mind” as to motive.

He said a suspected arson attack in the same road three weeks earlier wasn’t being linked to Sunday’s attack, but “we have a lot more research to go through”.

There were a number of a lines of enquiry but there was “no doubt” about the cause of the fire, he added.

He said petrol was poured through the letterbox on to the laminate flooring of the semi-detached house just before 4.30am.

It exploded, shooting a fireball - which could have eventually reached temperatures of up to 600 degrees Fahrenheit - upstairs where the family were sleeping.

Neighbours managed to break into the house through a back door but were beaten back by the flames, he said, but fire crews - who hosed water through the window in the front door - entered through the back door and rescued Jumaid, Nabiha and Maleha on the first floor.

Zain and his mother Rubina, 53, jumped from a first floor window. She was released from hospital on Monday.

Maleha’s Sister Nabiha, 21, who is a South Thames College student, was recuscitated by paramedics at the scene.

Brothers Zain, 22, and Jumaid 16, both attended the fee-paying Trinity School in Croydon.

Jumaid, who is said to be highly academic and wants to be a doctor, won a scholarship to study at the school.

Two teenagers, aged 14 and 15, have been arrested and bailed for the arson but, D Chief Insp Allain added: “I’m not hanging my hat on those arrests . . . people need to come forward with information.”

He added the attackers might have injured themselves lighting the blaze and police were checking CCTV from the area.

If you have any information call police on 020 8721 4805 or call Crimestoppers anonymously on 0800 555 111.