Today's Sun front page claims that over 1,200 people have been killed by "mental patients" in the past ten years.
The story quotes an academic report - the National Confidential Inquiry into Suicide and Homicide by People with Mental Illness, produced by the Centre for Mental Health and Risk at the University of Manchester. (As such, it's not so much an "exclusive investigation", more "reading a report on the internet that was published in July".)
The article says that the figure refers to "high-risk patients" who were "allowed to kill" by "failings in Britain's mental health system":
In other words, this figure explicitly includes people who were not patients at all, never mind the "high-risk" patients that The Sun claims.
The report is completely unambiguous about this:
In other words, almost half of those who committed the homicides that made up The Sun's 1,200 figure were not "mental patients", their illness cannot be shown to have caused the homicide, and for most of that group, the mental health system could have done nothing to prevent the death.
And even those that were classed as "patients" were not necessarily "high-risk" patients, as The Sun claimed - just anybody who had contact with the mental health system in the previous year. According to Paul Farmer, the Chief Executive of the mental health charity Mind, that's a figure of around 1.2million people.
We have asked the University of Manchester for a comment on The Sun's use of their research, and will update this article if they respond.
Update: Professor Louis Appleby, the report's lead author, has confirmed on Twitter that The Sun misquoted the figures, and gave more context for the study's findings:
As Professor Appleby says, the trend for homicides by both patients and those with symptoms of mental illness has been down in recent years:
The Sun's report also fails to mention another key figure in the Manchester study: in the same period that 738 mental health patients committed homicides, 13,469 patients committed suicide.