Dutch investigators suspect an Austrian man held a father and five adult children against their will for nearly a decade on a remote farmhouse before they were finally rescued, officials said on Wednesday.
The 58-year-old man, identified by media as Josef B., was arrested after police discovered the family of six in a tiny secret room in the building in the village of Ruinerwold in the northern province of Drenthe.
The mystery surrounding the case deepened with reports that the son who had reportedly walked into a bar and raised the alarm about their captivity had nevertheless been active on social media this year.
"In the investigation, the man is currently suspected of being involved in illegal deprivation of liberty and harming the health of others," Dutch prosecutors said in a statement.
The man will appear before an examining magistrate on Thursday who will decide whether he should be kept in custody for longer.
Police also raided two properties as part of the investigation, including a former toy store owned by the suspect in the town of Zwartsluis, 16 kilometres (10 miles) from Ruinerwold.
The Austrian foreign ministry earlier said an Austrian national from Vienna was being held in relation to the case, but said the man did not want to have contact with Austrian officials.
Ministry spokesman Peter Guschelbauer told AFP that Dutch authorities had informed their Austrian counterparts that all others in the cellar case were Dutch.
- 'We never saw anything' -
The mayor of Perg district in Upper Austria state said the arrested man had worked as a carpenter and lived alone for 10 years before leaving for the Netherlands in 2010, describing him as "reserved" and "discreet."
The man was reportedly known in Ruinerwold as "Josef, the Austrian" and Dutch media said he was the one who held the group, renting the house and planting vegetables for them in the garden.
"We used to see him, at first we thought he was our neighbour. And we always used to think that he lived alone there, that no one else lived there," Vincent de Gooijer, 46, who lived in a house overlooking the farm, told AFP.
"He was always busy working, we assumed he was doing up the farm. But he arrived early in the morning and left at the end of the afternoon, so he didn't sleep there or live there."
De Gooijer added: "I can't believe that such a thing is possible. And you know it's weird to say that we never saw anything all these years. But if these people never go out and they shut themselves away, there's nothing you can do."
According to media reports, the family had spent years "waiting for the end of time", although officials would not confirm that.
Police had earlier said they were held in a cellar but later said the family were kept "in a small room in the house that was closed off".
Ruinerwold's mayor told journalists: "I have never come across anything like this before."
- Social media presence -
The oldest of the children, a 25-year-old who has only gone by the name of "Jan", kept a Facebook account and posted an update in June for the first time in nine years, according to Dutch media.
"Started a new job at Creconat," popular daily tabloid De Telegraaf quoted him as saying. The timber company is affiliated to another in the nearby town of Meppel owned by the Austrian and was raided by police on Monday.
"Jan" also posted pictures of himself "surrounded by trees" in and near Ruinerwold, as well as links to products and rallies including the recent climate marches, the paper said.
On his profile on the jobs site LinkedIn, meanwhile, he wrote that his parents had run a successful business until his mother died in 2004.
Local news station RTV Drenthe, which first reported the story, said police were alerted after "Jan" walked into a village bar on Sunday evening.
The dishevelled man, unwashed and wearing old clothes said "he has not been 'outside' for the past nine years," bar owner Chris Westerbeek told RTV Drenthe.
The family were examined by a doctor and taken to a safe location.
While police investigate exactly what was going on at the farmhouse, the case has raised questions about how it took so long for anyone to notice that anything was wrong.
"People live far from each other here, they help each other when they need," Henk Udding, 64, who lives in a nearby village, told AFP.
"But when that's not needed, we leave other people alone."