By Jonathan Duffy
BBC News Online
On an ordinary working day last year, Dr Richard Stevens walked out of his office and vanished, without a word to his family. Six months later his body was found. Why do people vanish like this?
Dr Richard Stevens arriving at work, the day he went missing
Monday 21 July, 2003 started as a day like any other for Dr Richard Stevens. A respected medical consultant, Dr Stevens steered his Audi the short distance from his home, in the smart suburb of Sale to his work at the Royal Manchester Children's Hospital in Salford.
Walking into the hospital at 0710, the 54-year-old paediatric haematologist went to his office where he placed his briefcase on the floor, his security pass on his desk and his jacket over the back of his chair.
And then he vanished.
Nothing was heard of Dr Stevens until his body was found earlier this week, in a disused slate mine in the Lake District.
Police say it was not an accident and there are no suspicious circumstances.
To his wife of 31 years, Eirwen Stevens, the reason for his disappearance is a total mystery. The couple had enjoyed a healthy marriage and seen their children Jonathan, Helen and Rebecca grow up happily.
A man of many hobbies and pastimes, Dr Stevens had a pressured job
The recent arrival of a grandson was a new source of pleasure. But Dr Stevens' years spent looking after terminally ill children had been "extremely stressful", according to his wife.
Of the 210,000 people who go missing each year - most of whom return shortly afterwards - just a relative handful come close to the profile of Dr Stevens.
While missing children tend to grab the headlines, adult disappearances mostly fall into two categories - men aged 24 to 30, and elderly sufferers of dementia.
After 30 the proportion reported missing declines progressively as age increases, until senior years.
At the National Missing Persons Helpline (NMPH), cases such as that of Dr Stevens are loosely referred to as "professional disappearances".
"We have noticed a pattern of slightly older professional people, most often men, who go missing as a result of stress from a variety of sources, such family strains, financial problems or work related stress," says Jessica Prasad, of the NMPH.
Some are what's come to be known as "pseudocides" - so-called Reggie Perrins who fake their death to start a new life.
More perplexing, and concerning, are cases where people leading seemingly ordinary lives make a snap decision to wander off, and sometimes never return.
Nine years ago the comic Stephen Fry vanished while starring in a West End play that had been panned by critics.
"I suffered a dreadful attack of what golfers call the yips and actors call stage fright. For years I have been incapable of saying 'no' and have allowed my work to become my life," Fry explained, following his exile on the Continent.
Yet the question of adult disappearance is largely overlooked. Kym Pasqualini, who set up the Center for Missing Adults in America, says research is 20 years behind the issue of missing children.
Nina Biehal, co-author of a recent report looking at the reasons adults vanish, was stunned to find there had been no comparable research on the subject anywhere in the world.
The study found that grown men are far more likely to go missing than women, and almost two-thirds of adults vanished intentionally.
"In terms of middle-aged professionals, it is quite unusual, particularly for those aged 51-60, who account for just 5% of adult disappearances," says Ms Biehal.
Just some of the thousands of missing adults in the US
The most likely cause was multiple stresses - the term for a combination of work, family, financial and other pressures - which "could bring people, most often men, to a crisis where they suddenly leave home and disappear without trace".
Another possible explanation for "professional disappearances", and one which Dr Stevens' wife had seriously considered, is dissociative fugue - a form of amnesia which leads the victim to suddenly wander off.
"It's most commonly associated with the severe psycho-social stresses brought about by war or natural disaster," says psychiatry professor Ann Mortimer. Yet, in America, it has been said to affect up to one person in 500.
Given the stresses of modern life, are adult disappearances rising?
George Rivers, of the British Association of Investigators, doesn't think so. For adults to go missing for no apparent reason is rare, he says, but has always happened.
"People going off for no apparent reason is not something new. But I am quite sure that where there is no reason given publicly there is always a reason of some sort in the background, whether its money worries or matrimonial problems."
Even though we live in an age of CCTV and all-pervasive surveillance, Mr Rivers says it has actually become harder to trace people, because of the Data Protection Act. Employers and landlords hide behind the legislation making it difficult for investigators to do their job.