AMSTETTEN, Austria - Police say investigators are using a sonar probe to make sure there are no more underground dungeons at the property where an Austrian man held his daughter captive for 24 years.

Police official Leopold Etz says officers also are questioning more than 100 people who lived at some point in Josef Fritzl's house in Amstetten over the past two decades.

Police say the 73-year-old Fritzl has admitted holding his daughter Elisabeth captive and fathering her seven children.