Emma Winnall, 93, who was attacked in her home in Moseley, Birmingham, nearly a month ago, died this morning of complications arising from her injuries, West Midlands Police have said.
The great grandmother was attacked in her own bed between 9pm on 30 April and 9am the following morning, when she was found by her carer.
Superintendent Richard Baker, Head of Major Crime in Birmingham said that their investigation has now become a murder inquiry.
He said in a statement: "This is desperately sad news…our condolences go out to Emma's family and friends.
"Clearly, this has now become a murder inquiry. But given the extent of Emma's injuries, combined with her age and vulnerability, this investigation has always been treated with the same level of seriousness as a murder investigation."
"Two people remain on police bail having been arrested in connection with the assault. However, our enquiries continue and I'm still appealing for anyone with information to come forward and speak to us in confidence.
"This was a shocking attack on a defenceless, elderly woman as she slept in her own bed. No-one capable of carrying out such a despicable attack deserves protecting – I'm asking people to look into their consciences and if they have any suspicions about who may be responsible to contact police."
A woman, 56, and a 28-year-old man, were arrested at their home in the Hall Green area of Birmingham by officers from West Midlands Police on 18 May. They have since been released on bail.
The force said the dawn arrests were made after routine police inquiries and were not a result of information from the public.
Despite the developments, police urged anyone with any information to contact West Midlands Police on 101.
A reward of up to £5,000 has been offered by the independent charity Crimestoppers for anyone who contacts them on 0800 555 111 or via their website and provides information which leads to the arrest and conviction of the pensioner's attacker.
Mrs Winnall's daughter issued an emotional appeal for information after the attack.
Joyce Blencoe said: "It's broken my heart to hear my frail and defenceless mum in hospital manage to say she was screaming for help and no one came.
"To see your mum viciously beaten and covered in blood is the most horrific nightmare."
"Someone out there knows who did this, so please come forward before they do it to someone else," she said.
At the same media conference, Detective Chief Inspector Sab Johal said the "horrific" attack was a "unique offence".
Police have previously said the motive for the attack remains unclear, and they believe nothing was stolen.