'Why did you kill my dad?'

Philip Hendy was killed in a random attack by Stephen Newton

The number of murders committed by people with serious mental health problems in the UK could be more than double the number recorded by official statistics, a documentary has uncovered.

Filmmaker Julian Hendy spent nearly three years researching such murders after the killing of his father, Philip Hendy, in Bristol in 2007.

One Sunday morning in April 2007, my father was fatally stabbed in Bristol by a man with a long history of mental health problems.

He had just gone out to pay his paper bill and he never came back.

It was a completely unprovoked attack by a man my father had never seen or spoken to before.

I loved my father very much. He was a good and kind man who had a great sense of humour.

When he became a grandfather it was like he had a new lease of life. Constantly making things and always happy to play with his grandchildren, at 75 he still had everything to live for.

To lose a parent for any reason is hard enough, but to lose a parent to murder is incredibly difficult - particularly the thought that someone went out and intended to do serious harm to someone you love.

I wanted to understand how such a thing is possible - to try to come to terms with how my father could be killed this way, in the middle of a city on a sunny Sunday morning, just going about his everyday business.

Murders 'common'

I found many mental health professionals are often reluctant to talk about violence, often from the well-meaning (but in my view misguided) fear of raising "stigma" against people with mental health problems.

Stephen Newton was given a prison sentence of at least 16 years

But to my mind, ignoring a problem is no solution to it and it certainly does no favours to those seriously mentally ill people who do commit violence and who end up for long periods of their lives in prison or high security hospitals.

Professor Louis Appleby heads the National Confidential Inquiry into Suicide and Homicide by people with mental health problems, which records cases in England and Wales.

He told me: "There are about 50 cases a year, so that's 50 people who are convicted of a homicide, who in the 12 months before the incident, were in contact with specialist mental health care. They account for about 9% of all homicide convictions.

"The starting point for the confidential inquiry is conviction, so we focus on the perpetrators.

"So for example, if somebody was responsible for a homicide in which there were multiple victims, that would count as one incident from our statistics.

"So the 50 cases a year is perpetrators, not victims.

"And of course, there are a small number of cases where a person commits homicide and then commits suicide so there is no conviction so those cases aren't included in our 50 cases a year."

But in talking about perpetrators, we do not see the full picture of how many victims there are.

And it is hard to discover a figure for the total number of people killed each year due to mental health homicide because cases where there are multiple victims, or where the killer commits suicide afterwards are under-represented (or don't feature at all), and figures for Scotland are published separately.

But after all my research for the film, I discovered mental health homicides are actually quite common in Britain - around two a week - about 100 or so a year.

The mental health charity Mind was asked to comment on the programme's findings.

Chief Executive Paul Farmer said: "There are around six stranger homicides by people with mental health problems a year, yet over a third of the public think that people with mental health problems are prone to violence which is hugely disproportionate to the actual risk.

"In fact, research shows that people with a mental health diagnosis are far more likely to be the victims of crime than the perpetrators."

Recurring failures

The killings do not just affect those who are killed.

It affects their families, their friends, and often whole communities - dozens of people traumatised by a single mindless act.

I know the vast majority of people with mental illness are never violent, but it's undeniable that some are

And homicides are just the tip of the iceberg.

Last year there were more than 38,000 physical assaults on NHS staff in mental health services - the highest rate for any sector of the NHS. Yet some campaigners still maintain violence by the mentally ill is a "myth".

But one of the most shocking things I discovered is that many mental health homicides have a background of very similar problems.

The same problems have been warned about since 1994 and still keep occurring today.

Record keeping, care planning, treating drug problems, listening to the family and doing risk assessments crop up time and time again with depressing frequency, yet nothing effective ever seems to get done to deal with the problem.

In the Bristol area, where my father was killed, there have been at least 22 mental health homicides since 1993.

They have resulted in some four inquiries, which have all raised these concerns and each time an action plan and new policy would be written, yet exactly the same problems would crop up in the next mental health killing - as they did in my father's case.

I think mental health services need to demonstrate that they can truly learn from these tragedies.

I know the vast majority of people with mental illness are never violent - but it is undeniable that some are.

I think we need to talk about the problem in an open and honest way rather than pretending it doesn't exist.

Why Did You Kill My Dad? was broadcast on Monday 1 March, at 2100 GMT on BBC Two and is available on the BBC iPlayer