(Agencies)
Updated: 2008-05-05 23:32

AMSTETTEN, Austria -- Police say the Austrian man accused of holding his daughter captive for 24 years planned to build his secret cell as early as 1978, when she was just 12 years old.

Investigators also say a total of eight doors secured the underground warren of windowless rooms where Josef Fritzl imprisoned his daughter at 18 and fathered seven children with her.

Prosecutors told reporters Monday in the town of Amstetten, west of Vienna, that they will have their first meeting with Fritzl this Wednesday or Thursday.

The 73-year-old suspect has not yet been charged, but his lawyer has said he is preparing an insanity defense.