Concerns about health service resources for patients with personality disorders have been raised in a report into 11 killings in the East of England.
The report commissioned by NHS East of England looked at 11 mental health service patients convicted of killings.
The report's authors highlighted resources and the quality of internal investigations as concerns.
A spokesman for NHS East of England said robust action plans were in place and significant progress had been made.
The reporting team considered the effectiveness of the services offered to patients treated by the Hertfordshire, North Essex, Cambridgeshire and Peterborough and Bedfordshire and Luton NHS trusts.
After reviewing the cases, which all took place between 2002 and 2006, the report team expressed concern about the "adequacy of resources to meet the needs of people with personality disorders".
It added that the lack of resources was not a "causal factor in the homicide".
The team also criticised the quality of some internal trust investigations.
An NHS East of England spokesperson said: "NHS East of England would like to express its sincerest sympathies to all concerned in these tragedies.
"The trusts have submitted robust action plans and significant progress has already been made."