Police say that given the extent of Mrs Winnall's injuries, her age and her vulnerability, their investigation had always been treated with the same level of seriousness as a murder inquiry.
Officers managed to speak to the 93-year-old in hospital in the days following her attack.
West Midlands Police have appealed again for information following the death of pensioner Emma Winnall nearly a month after she was attacked at her home in Birmingham.
Superintendent Richard Baker, Head of Major Crime at the force, renewed their appeal in what has now become a murder inquiry.
This is desperately sad news. Our condolences go out to Emma's family and friends.
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.
Emma Winnall had been in intensive care since May 1 after being found badly injured in her bed.
She suffered a fractured skull and broken arm in the savage attack.