A Newcastle care home was unaware of an elderly resident's violent history until she battered a fellow resident to death, a report has concluded.
Thrower had spent time in Rampton Hospital
May Thrower admitted manslaughter on the grounds of diminished responsibility in June, after attacking 93-year-old Olive Garvie with an iron.
Thrower, 83, had a history of violence, and had spent 17 yeas in Rampton high security hospital.
An inquiry has found vital records were lost, not kept or destroyed.
Thrower was living at the Coniscliffe residential home when she battered Mrs Garvie at least a dozen times with an old-fashioned iron in February 2004.
It emerged during her subsequent trial that Thrower was suffering personality disorders, involving "paranoid, schizoid or dissocial features".
She had also attacked elderly neighbours, had other convictions and was known to Northumbria Police.
After the court case, Newcastle City Council ordered an independent inquiry to establish how Thrower came to be living in a care home with no nursing staff aware of her medical history.
The report, by neighbouring Sunderland City Council, found that although Thrower had a history of psychiatric illness, she had shown no evidence of this for some time and that "no single agency was in full possession of the facts" surrounding her background.
It said: "Records were either not kept, lost or destroyed in accordance with the criteria of the relevant agency."
Catherine Fitt, Newcastle's director of social services, said: "The key lesson has to be that agencies must establish procedures and systems to share information.
"In retrospect there was information which should have been shared which might have helped prevent what is a unique and tragic incident."