A woman who was killed along with her four children when their home was set alight may have been having marriage problems, police have revealed.
Mrs Riaz and her daughters died in their beds from smoke inhalation
Caneze Riaz, 39, and daughters Sayrah, 16, Sophia, 15, Alicia, 10, and Hannah, three, died of smoke inhalation at the house in Accrington, Lancashire.
Officers are still waiting to question her husband Mohammed, who is critically ill in hospital.
He has been named as the "top line of inquiry" in the murder investigation.
All five victims were already dead in bed when fire crews broke into their home in Tremellen Street in the early hours of Wednesday.
Mr Riaz was also pulled from the house by firefighters and is now being treated in a specialist burns unit at Wythenshawe Hospital in Manchester.
He has reportedly suffered 50% burns to his body and remains in a critical condition.
Forensic examinations of the house revealed that whoever started the blaze did not leave the house.
Accelerants were used to start several seats of fire and all of the windows and doors were locked from the inside.
On Thursday, Lancashire Police revealed they were examining the possibility that Mrs Riaz, described as a "pillar of the community" may have grown apart from her husband.
Police revealed whoever set the fire did not leave the house
Det Supt Mick Gradwell, leading the inquiry, said: "We are now investigating a line of inquiry that there has been a breakdown in the relationship between Caneze and Mohammed Riaz."
Special assemblies have been held at Hyndburn Park Primary School, where Alicia was a pupil, and at Accrington Moorhead Sports College where her two elder sisters studied.
Andrew Bateman, head teacher at Accrington Moorhead Sports College, said: "Everyone came together, 1,000 staff and pupils, to share their grief together. It was very calm and quiet."
As well as the assembly, the college has been providing individual and group support to help students try to come to terms with the tragedy.
Mourners have laid dozens of floral tributes outside the house where the four girls and their mother lost their lives
A book of condolence has been opened for the family at Accrington town hall.