Berlin (CNN)It was the evening of July 5 and Magdalena Freudenschuss hadn't heard from her partner all day. That was unusual, so she was worried.
Peter Steudtner, a human rights trainer, was at a workshop on IT security and mental health strategies for activists in Istanbul with several colleagues.
"We made calls to Turkey to find out what had happened, whether it was just an internet problem," Freudenschuss told CNN. "And then we found out through the consulate."
Steudtner had been detained along with another trainer and eight human rights activists, including the director of Amnesty International in Turkey, Idil Eser.
Three weeks later, all of them -- now known as the "Istanbul 10" -- remain in custody, accused by Turkish authorities of "committing crimes in the name of a terrorist organization without being a member."
Freudenschuss was allowed a brief phone call with Steudtner soon after his arrest, but "he couldn't tell me a lot," she said. "At that point we didn't foresee how long it would take."
At first, Steudtner and the others were kept in solitary confinement, but they have since been put together in one cell, Freudenschuss said.
He has started a yoga routine and leads his cellmates in classes, according to Freudenschuss' family representative.
But Freudenschuss knows little else about the conditions in which Steudtner is living, and can contact him only via messages passed on by his lawyer.
Freudenschuss and Steudtner, who live in Berlin and have been together for 10 years, have two children together.
"It's hard for them as well," she said. "There is a father missing, there's someone missing who reads books to them, who listens to me, to the kids."
The Turkish government has not responded to CNN's request for comment. But presidential spokesman Ibrahim Kalin last week defended the decision to detain the activists.
"They are people who according to the police and the judiciary are engaged in illegal or suspect actions," said Kalin, who called for Germany to "respect Turkey's judicial independence."
Arrests are 'a threat for everyone'
The allegations against the activists are "unjustified and obscure," said Markus Beeko, secretary general at Amnesty International in Germany told CNN.
"The Turkish authorities have used absurd allegations to try to justify this breach of international human rights sta