Police are investigating why a man was kept confined inside his home for three decades. Photo / Getty Images
It's hard to know exactly what went on inside the home of a German family in a quiet village near Bayreuth.
For almost three decades their son was kept from the outside world. He left school one day aged 13 and wasn't seen again until now, aged 43, looking "unkempt but well nourished", according to police.
The man cannot be named because of Germany's strict privacy laws, but local media is reporting he lived at home with his parents, both aged in their 70s.
The man's mother says she wasn't holding him against his will. Instead, he simply "didn't want to go out".
What at first glance appeared to be a hostage situation could be much more complex. Experts and former sufferers say if long-term agoraphobia is to blame, as the man's parents suggest, the situation is surprisingly common.

Police received a tip-off about the goings-on inside the house in the Bavarian town 230km north of Munich in September.'HE HAD SEVERAL ROOMS TO HIMSELF'
When they knocked on the door, they found the man in reasonable health and able to move around the home freely.
"The man was unkempt, unwashed, but well nourished," police spokesman Juergen Stadter said.
"He wasn't constrained and had several rooms to himself where he could move around."
Stadter said the man went to a local school when he was 13 but was declared unfit to continue attending. The officer did not give further details, but several outlets are reporting the 43-year-old was a victim of bullying in his early teens.
"We assume he was suffering some kind of handicap," Stadter said.
The man's mother said once her son described his wishes to stay indoors, she "always wanted to protect him".
Justin Kenardy, Professor of Clinical Psychology at the University of Queensland, has treated hundreds of people suffering from agoraphobia, a mental illness described as an extreme or irrational fear of open or public places.
He told news.com.au he was not surprised when he read about the German case.
"If it's 25-30 years, that's on the more extreme end, but it's not that surprising. I've seen cases where people stay in their house for longer than that."
He said if the man was bullied and suffered a panic attack, that could easily trigger the condition.
"A panic attack or maybe several panic attacks are often where it starts. What happens is the person tries to identify what it is about their environment that caused the anxiety.
"They will go from avoiding the situation they were in - maybe they were in the supermarket, or walking down the street - to becoming more and more concerned about places and situations that may lead them to become more panicky."
Professor Kenardy said parents, family members and friends who enable agoraphobia do so out of a "genuine sense of wanting to care for and protect the individual", as misguided as that approach may be.
He said the condition is actually very treatable, and he's seen dozens of cases where sufferers have completely turned their lives around.
"With really good cognitive behaviour therapy, the success rates are really, really good."
Veronica Allen lived with the condition and recovered, but told news.com.au it was a hard fight.
"A few panic attacks" was all it took to turn Veronica Allen, a normally active woman, into a person she did not recognise.
She said she struggled with the simplest things and was confined to one room for a number of years.
"As a result of my agoraphobia, I developed severe anxiety attacks, stopped eating, found it hard to watch TV, read the paper, answer the phone," she told news.com.au.
"I was a prisoner inside my own body, it was hideous."
She said it started out slowly then increased without her realising what was happening.
"Becoming fearful of going outside gradually escalated to severe - so severe in fact that even going into other rooms within my house would bring on an attack.
"I eventually sat in my lounge chair and would only leave it if I was not at home alone."
Ms Allen, from Geelong in Victoria, said during her most difficult days she read a story about a woman who was too scared to go to her letterbox. It was the first time she'd heard of agoraphobia.
"I eventually sought help with counselling, became involved in a group with others that had the same illness, some less severe however any level is debilitating. The tools they introduced, like blowing into a paper bag, didn't work for me or seem practical so I developed my own."
She started carrying a small crystal as a distraction and a water bottle to help focus her thoughts. Day by day she emerged from the house, moving further out into the outside world each time.
"Getting myself back outside was a slow process but started with stepping out onto the step and standing there for as long as I could cope then doing the same thing each day, taking a step further each time. I'm completely over it now."
Ms Allen has written a book about her experience - Fractured Mind - and hopes others going through the same thing seek help.
The Australian Government's Department of Health says 1-2 per cent of Australians live with a panic disorder and women are twice as likely as men to experience it.