ST. POELTEN, Austria — Josef Fritzl abruptly pleaded guilty to all of the charges against him Wednesday — a surprising twist amid disclosures that Elisabeth, now 42 and the daughter he imprisoned for 24 years in a dungeon where she bore him seven children secretly sat in on the trial.

Fritzl calmly acknowledged his guilt, including to homicide, and said his change of heart came after hearing his daughter’s heart-wrenching videotaped testimony. “I declare myself guilty to the charges in the indictment,” Fritzl, 73, told a panel of judges, referring to what he called “my sick behavior.”

Fritzl was charged with negligent homicide in the death of an infant boy as well as enslavement, rape, incest, forced imprisonment and coercion. Initially, he pleaded guilty to incest and forced imprisonment, and partially guilty to rape and coercion. The change means he could face up to life in prison for the homicide charge.

Verdicts and sentences were expected today.