Two men and a women, suspected of having connections to the kidnappers, have now been detained by the Solna district court for extortion, kidnapping and preparing to commit murder.
Prosecutor Krister Petersson says he believes that fleeing Eritreans were kidnapped, and then people in Sweden demanded money. He says similar crimes have been reported.
But reporting such crimes is unusual, because many people fear revenge. According to Swedish-Eritrean information, hundreds of families in Sweden have been extorted by kidnappers on the Egyptian Sinai Peninsula. Other countries have also collected similar reports.
A UN report from 2012 described how high-ranking Eritrean military officers allied themselves with kidnappers and were earning many millions of Swedish kronor through these methods and also through weapons trade.
A few months ago, a woman living in Sweden found out that her 16-year-old brother had been kidnapped in the Sinai. From there, his kidnappers called her brother and sister in Eritrea. She tells TT, "They rang once every half-hour while they beat him and demanded SEK 242,000."
"We were forced to pay to save his life," she says.
Investigators from the UN have been in Sweden this week, gathering witness testimonies from Swedish Eritreans. They are also interested in how Eritrea demands taxes from Eritreans living in exile. Even this happens through threats and blackmail, according to the UN.
A UN resolution challenges member countries to prevent this collection, and the UK and Germany have agreed to for the time being, but not Sweden.
"The Dawit Isaak question holds Sweden hostage," says a person who is following the issue and wants to remain anonymous. "He is important, but come on, he is just one person. The price is that people are threatened and extorted."
Swedish foreign minister Carl Bildt dismisses the idea that Sweden is paralyzed on the matter of taxation. He says that in principle, it is difficult to stop, because it is not illegal for countries to collect taxes from abroad.
Bildt says that these cases, where the methods for collecting taxes are illegal - such as threats and extortion, are matters for the prosecutors and the police to dedicate themselves to fighting.
Eritrea maintains that the taxes are voluntary.