Depraved father Josef Fritzl, convicted after imprisoning his daughter Elisabeth for 24 years, is being investigated over at least four unsolved murders and disappearances.

Even as he was led away to prison, police were re-examining missing person and unsolved murder cases over the past four decades.

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One is the 1986 murder of Martina Posch, 17, who was raped, strangled and dumped in a lake a short distance from where Fritzl and wife Rosemarie ran a guesthouse.

"What really stands out is that Martina looks similar to Fritzl's daughter. The likeness is incredible," police chief Alois Lissl said.

Other cases include the shotgun murder of Anna Neumayer, 17, near Fritzl's workplace in 1966 and the disappearance of Julia Kuehrer, 16, near his home in 2006.

The investigation also includes sex worker Gabriele Superkova, 20, was murdered and dumped in a lake near where Fritzl was holidaying in 2007.

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