This is a chart of a particular kind of imprisonment; a kind of imprisonment where someone takes a person and turns them into an object, annuls their freedom, and keeps them for an extended period of time. Based on media coverage, I have found sixteen such victims over the past forty years.

Extrapolating from this chart, there are approximately ten people currently imprisoned, undiscovered, in this way.

"It's beyond creepy," he said. "This takes the cake. Trauma is like throwing a big rock into a pond. The waves go out and we are all sadly traumatized."

In the space of only two hours, Elisabeth told the story of her 24 years in captivity. At 12:15 a.m., when the officers completed the three full pages of minutes of the interrogation, they knew that it would be the most important case of their lives.

Both Steven Booth (myself) and Stefan Fritzl were born in 1990. This instantly drew a connection between us. He jumped out of being an element of a distant tragedy, and became someone. I had a way of understanding him. Suddenly every moment in my life became twinned with his. While our lives so far were dramatically different, we shared, as humans, similar fundamental psychologies, at similar times. For every thought I had, he had one too. I see my own stilted handwriting in his.

Stefan wrote, two months after his release: 'I miss my sister. Am enjoying freedom and my family. / I like the sun, the fresh air and nature.'

They did have some connection with the world outside — through an old television set. It was reality, but for the children living in Fritzl's basement, it was like watching a film. Images of meadows, mosquitoes and the sun might as well have been parts of some fantasy Never-Never Land, because these children had never smelled the scent of a meadow, felt the itch of a mosquito bite or the warmth of the sun on their skin. And the cars, spaceships, mobile phones and lightsabers? Couldn't all of this have been nothing but science fiction?

Elisabeth has always taken care of things for the sake of the family. I have tried to provide for my family in the cellar as best as possible. Whenever I went to the bunker I would bring my daughter flowers and cuddly toys as well as books for the children. I would watch an adventure film on video with them while Elisabeth would prepare our favourite food and then we would all sit together at the kitchen table and eat together.

I always knew during the whole 24 years that what I was doing was not right that I must have been crazy to do such a thing, but still it became a normal occurrence to lead a second life in the cellar of my house.

Ms Sano told police that at first she had been scared but eventually gave in to her fate. She said she had spent most of her time watching television.

"I was too scared to escape and eventually lost the energy to escape," the woman was quoted as telling police.

In her terror, she reportedly found it impossible to leave even when the man left the home, which was only a few steps away from other houses in the quiet neighbourhood.

The door, reports said, was never locked.