An Austrian judge ruled Friday that a man suspected of keeping his daughter captive in a dungeon for more than two decades should remain in custody, an official said.

The decision extends Josef Fritzl's pretrial detention by a month, St. Poelten provincial court spokesman Franz Cutka said. It was made during a routine, closed-door session required under Austrian law and will be re-evaluated in June.

• Click here to see photos of Josef Fritzl and the "House of Horrors."

Fritzl's lawyer, when reached for comment, declined to immediately provide a reaction.

Fritzl, 73, was formally placed in confinement April 29. He had been detained three days earlier on suspicion of locking up his daughter Elisabeth for 24 years and fathering her seven children.

Authorities say Fritzl has confessed to locking up his daughter and repeatedly raping and impregnating her. Investigators say he also told them three of the children were raised in a cellar at his home in Amstetten, three others were brought up above ground, and one died in infancy.

He is expected to be charged once investigations are completed. In Amstetten, west of the capital Vienna, detectives continued to comb through the vast Fritzl property for evidence.

Fritzl's alleged double life began to fall apart when Elisabeth's oldest child, a 19-year-old woman, was hospitalized with a severe infection.

Unable to find medical records for the woman, doctors appealed for her mother to come forward. Fritzl accompanied Elisabeth to the hospital April 26 and was detained after she divulged what had allegedly happened to her.

In comments relayed through his lawyer and published in the Austrian magazine News on Thursday, Fritzl was quoted as saying he knew it was wrong to hold his daughter captive and that he "must have been crazy" for doing so. He added that he tried to care for her and their children as best as he could by taking them flowers, toys and books, according to the interview.