THE parents of a Chesham man who was killed by a paranoid schizophrenic feature in a ground-breaking documentary focusing on mental health issues next week.

Jim and Judy Cargill speak about their experiences with dealing with mental health trust officials following the death of their son Ben in 2004.

Ben was stabbed to death by Robert Browning in Lowndes Park while watching a music concert. It was the day before his 25th birthday.

His killing is one of four covered by the film, 'Why Did You Kill My Dad?', which will be shown on BBC2 on Monday night.

It was made by documentary maker Julian Hendy, whose father Philip was also stabbed to death by a man with mental health problems.

Mr and Mrs Cargill, of Rose Drive, Chesham, said they were more than happy to take part in the film.

Mrs Cargill, a 58-year-old school lunchtime supervisor, said: “We wanted to do it for Ben, that was the main reason. We felt we wanted to do all we could for Ben.

“When the letter dropped on the doormat I thought, 'Thank you'. It's just a shame it had to happen to Julian's dad for him to be doing this film.”

Husband Jim, a 63-year-old gardener, said: “We both said, 'Perhaps this is what we are waiting for'. It was something that came at the right moment. To try and do anything on your own is like banging your head against a brick wall.”

Research in the documentary suggests 50 homicides a year are caused by people known to mental health services – but experts believe the actual figure is at least twice that.

Robert Browning was detained indefinitely under the Mental Health Act in 2005 – but was released just three years later.

Mr Cargill said he hoped the film would lead to changes in how cases like Browning's are dealt with.

He said: “He [Browning] did what he did but our argument is he should never have been allowed to do it in the first place because they knew about him. The big problem isn't him, it's that the system doesn't actually work.

“Hopefully there will be changes but we don't think they will happen very easily. It will be a fight, but it shouldn't be.”

Mrs Cargill added: “They keep saying lessons have been learned and that makes me feel angry. It doesn't mean anything, it's just words. If lessons are being learned, why is this still happening?”

The couple were approached by filmmaker Julian Hendy after he read about their story on the Bucks Free Press website.

Mr Hendy said his motivation for making the film was because he didn't want the same thing to happen to anyone else.

He said his father's killing “wasn't a one-off”, adding: “It has happening far more often than was commonly acknowledged”.

* 'Why Did You Kill My Dad?' is shown at 9pm on BBC2 on Monday March 1.