A man serving an eight year prison sentence for attacking his former partner could be charged with murder after she died at the weekend.
Kathryn Cook, 44, never regained consciousness following the assault, having spent the last eight months in a coma.
Ms Cook's family were at her bedside when she died at Bishop Auckland General Hospital.
Last week Paul Northey, 39, was jailed by a judge at Durham Crown Court having admitted a charge of causing grievous bodily harm with intent. But now he could be charged with murder.
Detective Superintendent Ken Donnelly, of Durham Police, said a post-mortem examination was due to be carried out by a Home Office pathologist.
"When we have the conclusions of the pathologist we will consult with our colleagues at the Crown Prosecution Service for advice on what further action should be taken," he said.
Chris Enzor, the chief crown prosecutor for Durham, said: "We would certainly give serious and careful consideration to any report submitted to us by Durham Police."
Ms Cook was found lying on her bed with a severe head injury by her 10-year-old daughter Rebecca at their home in Penshaw Gardens, Stanley, County Durham, on June 25 last year. Rebecca ran to her grandparents nearby to tell them she could not wake her mother.
Northey, who lived nearby in Wylam Road, Stanley, and Ms Cook had a volatile relationship. Northey would attack her by tearing hair from her head, and when police examined the crime scene after Ms Cook was found badly injured, they found clumps of hair in her bedroom and also in Rebecca's room.
Although the couple had split up after a seven-year relationship they would still meet secretly.
