Mary Fox, 59, was trapped in her bedroom after reportedly pushing her 17-year-old son Raum to safety through an upstairs window.
Officers are investigating claims that Raum, who has learning difficulties, was being bullied at school and that the family had been targeted by youths who had been throwing fireworks in the street.
Police said they had launched a murder investigation after the remnants of a firework were found behind the front door of Mrs Fox's house in Carpenter Court, Bodmin, in Cornwall.
Last night, Mrs Fox's family paid tribute to their "loving and caring" mother who devoted her life to her children and "would give her last penny" to help people in need.
A team of officers conducted house-to-house enquiries yesterday and collected the remains of fireworks found in the street for potential evidence.
After leaping from the three-storey house Raum ran to alert neighbours that his mother was still trapped inside.
He was taken to Treliske Hospital where he was treated for smoke inhalation and he was being looked after last night by his eight brothers and sisters.
Firefighters arrived within minutes of a 999 call at around 7.15pm on Thursday. They found Mrs Fox dead in the same room from where her son escaped.
Speaking at a press conference at Bodmin police station yesterday, Superintendent Martin Orpe warned the people responsible that police would find them.
"I am appealing to those people involved in this to do the decent thing and come forward to the police," he said.
"If not, I am confident from what I have seen that we will be knocking on their doors shortly.
"I would ask them to come forward, and anyone who knows fact in relation to this incident - not rumour, because there is a lot of rumour going around Bodmin - to come forward."
Mr Orpe said police were "following up leads that the family were being targeted" and are speaking to the school attended by Raum over allegations that he was being bullied.
Police later issued a statement confirming the Fox family had made no complaints about harassment to the Devon and Cornwall force.
Superintendent Orpe said: "The police can confirm that they have had no calls to the address in relation to any incident regarding bullying or intimidation involving the occupants."
Police said there were many people around at the time the fire broke out attending a nearby organised bonfire and fireworks display.
Senior investigating officer Detective Chief Inspector Paul Burgan said there had been speculation about those responsible posted over the internet.
"We are keeping an open mind at the moment. There are names being bandied around on social networking sites but this is innuendo. We need to deal with factual evidence and get the information direct.
"I would say to them that if it was a harmless prank please come forward.
"A lot of people will give us information and we will find those individuals responsible, so it would be in their interests to come forward at the earliest opportunity."
In addition to Raum, Mrs Fox had eight other children aged between 20 and their mid-thirties.
In a statement, the family said: "We, the sons and daughters of Mary, would like to thank everyone for their kind words at this difficult time.
"We would also like to say a huge thank you to the fire service who tried to rescue our mother from this horrific fire that makes no sense.
"Our mum devoted her life to us her nine children and went without herself to provide the best that she could for us.
"She was at times, shall we say, eccentric, she had a sense of humour and was loving and caring.
"She never did anything to hurt anyone and never would. She would give her last penny to help those in less fortunate circumstances than herself."
Flowers were left at the burned-out house in tribute to Mrs Fox.
Neighbours said Mrs Fox may have been trying to save her cat when the fire took hold.
Kerry Ollerenshaw, 36, said: "Mary was a little, polite, nice old lady that I would say hello to.
"She had a cat. People say that her son had learning difficulties, he was constantly with his mum.
"Everyone is shocked because you do not expect this to happen.
"But this isn't a bad estate, it is no worse than any other estate anywhere else in the country, you get bad apples everywhere."
Neighbour Doreen Rowe, 59, told the Western Morning News: "I'm devastated about what has happened, Mary was a dear old soul and a hero.
"There was loads of kids on the street armed with fireworks.
"She was not the only one targeted because my next door neighbour had one thrown at her house too."
Brett Millington, 17, said Raum had recently moved from Bodmin College to St Austell College because of bullying.
"He was badly bullied. It wasn't all physical but a lot of psychological abuse he suffered," he said.
"When he was at Bodmin, his mum would walk him to school every day because the bullying was so bad. But if anything, that just made it worse."
Following a meeting last night between representatives from Bodmin College, St Austell College, social services, mental health, housing, children's, schools' and families' services, Mr Orpe said there was no "obvious evidence" that either Mary or Raum had been victims of bullying.
He said: "Initial enquires have revealed that there are no mental health issues in relation to either the deceased, Mary Fox, or her son Raum.
"However, it is fair to say that Mary could have been regarded as eccentric.
"In relation to evidence of intimidation and bullying towards either Mary or Raum, again there is no obvious evidence that has come out of this meeting.
"To suggest that earlier press reports regarding the systematic intimidation or bullying of either of them was a cause of this incident is purely speculation and is unfounded at this time."
Witness are asked to call police on 08452 777444 or Crimestoppers on 0800 555111.
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