Austrian authorities say they took incest-imprisonment suspect Josef Fritzl back to his house as part of a police reconstruction of his alleged crimes.

Fritzl has been in custody since April, when he was arrested for allegedly imprisoning his daughter for 24 years and fathering seven children with her in a dungeon police say he built beneath his home.

Prosecutors have confirmed that Fritzl was brought under heavy police guard back to the house in Amstetten, west of Vienna, on Thursday. Officials say the visit was partly to determine whether the concrete-reinforced steel door to the cell could be opened from the outside.

Fritzl's lawyers insist his captives could leave. But investigators say the door could be sealed off with metal bars.