“Prosecutors have asked for another week because apparently there are some questions about the man's identity,” said Uppsala police spokesperson Christer Nordström to the TT news agency.
Police suspect that the man may be younger than the age he previously gave to investigators.
“Information has come up during the investigation indicating as much, so we have to dig a little deeper,” added Nordström.
Meanwhile, school inspection authorities are demanding to know how the children's absence from school managed to go undetected for so many years by local education officials in Uppsala.
The man's four children are currently between the ages of 16 and 22-years-old.
“It's serious that the children were kept out of school. We want to investigate what the reasons were. Has the municipality neglected its duties? The municipality has a responsibility to make sure that children like this who are required to be in school are actually in school,” said Ingegärd Hilborn, the head lawyer with Sweden's schools inspection agency, Skolinspektionen, to TT.
The agency expects a response from Uppsala municipality by the end of the week.
If officials in Uppsala are unable to explain the lapse to the satisfaction of Skolinspektionen, the agency can demand the municipality change its procedures to protect against similar cases in the future.
The father at the centre of the investigation is currently being held on suspicions of illegally imprisoning his family in their home and of gross violations of a woman's integrity.
The man was arrested in late June following complaints from neighbours about a disturbance in the family's home.
A few days later his wife filed for divorce, claiming she had been tortured by her husband and that had beaten her and the couple's children for more than 20 years.
The woman also requested that she be given sole custody of the two of the couple's children who are still under 18-years-old.