FACTBOX: Austria's house of horrors

(Reuters) - A 73-year-old man has confessed to holding his daughter captive in a secret, windowless cellar in the Austrian town of Amstetten for 24 years, and fathering her seven children, police said on Monday.

Here are the main facts about the case:

IMPRISONMENT:

Elisabeth Fritzl, now 42 years old, disappeared in August 1984.

She says her father Josef lured her into the cellar of their house, drugging and handcuffing her before imprisoning her.

Her parents then received a letter in her handwriting saying they should not search for her.

From 1984 until now, Elisabeth was kept locked in the basement and abused by Josef, who fathered her seven children, the youngest of whom is 5 years old.

The police say they believe Elisabeth's mother Rosemarie was unaware of what was going on.

CHILDREN:

In captivity, Elisabeth bore seven children over the course of 14 years, one of whom died.

Three of them remained imprisoned with their mother in the dungeon and never saw daylight. They are Kerstin, a daughter of 19, who was taken to hospital this month after becoming very ill, and two boys, Stefan, 18, and Felix, 5.

The other three were taken in and raised by Elisabeth's parents, Josef and Rosemarie. The first, Lisa, now 15, was supposedly left on the doorstep in 1993 along with a letter from Elisabeth saying she could not care for her. In later years another girl and a boy followed -- Monica, now 14, and Alexander, 12.

Alexander had a twin who died. Police say Josef has confessed to burning the child's body.

HOW DID THE CASE COME TO LIGHT?

This month, Kerstin was taken to hospital in Amstetten with a serious illness. Police made an appeal for information from her mother, the "missing" Elisabeth.

In response, Josef let Elisabeth, Stefan and Felix out of the basement. Elisabeth agreed to make a statement about her ordeal to the police after getting assurances that she would have no further contact with her father.