Detectives are investigating how a female carer died after suffering head injuries in the flat of a 95-year-old patient who is believed to suffer from dementia.
The elderly man, who neighbours said was frail and uses a walking stick, has been arrested on suspicion of murder.
Two ambulance crews arrived at his first-floor flat in Islington, north London, on Thursday morning after a neighbour heard a scream at around 4am.
Colleagues said they were left "devastated" after the woman, 61, died in hospital on Friday morning.
Scotland Yard detectives believe the victim was injured in the flat, where she was working as a carer for London Care, an agency commissioned by Islington Council.
A post-mortem is yet to determine her cause of death, but her next of kin have been informed, police said.
Max Wurr, senior spokesman for the woman's employer, said: "We were devastated that a member of our care team in Islington has died in hospital after paramedics were called to the home of one of our customers overnight.
"The cause of death has not yet been confirmed to us and we are assisting the police whilst their investigations are ongoing.
"Our thoughts are with the care worker's family and friends as they deal with this tragic news."
The 95-year-old man was taken to hospital as a precaution after being arrested on suspicion of murder.
The Metropolitan Police said he was granted bail but will remain in hospital until he is moved to somewhere "his complex health and care needs can be managed".
Detectives are not looking for any other suspects in connection with the probe.
A neighbour who has been living in the 95-year-old's block of flats in Holloway for 10 years said he was rarely seen outside his home since he and his wife fell ill.
The woman, who did not want to be named, said another neighbour told her of hearing a scream in the early hours of Thursday morning.
She said the elderly man would normally have a carer looking after him and he was occasionally visited by family members.
"It's a surprise. They are a very good family," she said.
"I don't know what's happened. I was coming home from work and saw police upstairs.
"Another neighbour heard a scream at about 4am, but I didn't."
Richard Watts, leader of Islington Council, said: "We are devastated to hear of the death of a carer in Islington.
"Our thoughts are with her family and friends at this desperately sad time."
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