Forensic experts have been carrying out tests in a bedroom to find out how a woman of 94 suffered severe facial injuries.
Police are treating the incident as suspicious but Detective Inspector Graham Pratt, heading the inquiry, admitted: "It is not so much a 'whodunnit' as a 'what happened'."
Staff at St Bede's Residential Care Home in Sackville Gardens, Hove, discovered the victim injured in bed in the early hours of Wednesday.
She had a broken nose, black eyes and other serious facial injuries.
There were no signs of a forced entry at the home and nothing had been taken from her room.
Blood patterns found in the room are being examined by scientists and a Home Office pathologist has been called in to study the woman's injuries.
The woman is in Brighton General Hospital, where her condition is described as "satisfactory".
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