We may never know what moved Wolfgang Priklopil to approach a tiny, 10-year-old girl on the street and take her as his own.
He kept her locked away in a makeshift dungeon in a normal neighbourhood in Vienna, Austria, for eight long years. She was his sex slave before she made a daring escape.
The day she left, August 23, 2006, Priklopil ended his life. He threw himself in front of a train and any answers about his motivations died with him.
In August, his victim Natascha Kampusch told her story for the first time. It provided some answers.
More are expected on Channel Seven's Sunday Night program this week as reporter Rahni Sadler ventures inside the dungeon where the small girl spent her teenage years.
She says the experience "creeped me out" but helped her understand what life must have been like for Kampusch and how she made it through.
"She walked us through the entire house and it was absolutely chilling," Sadler told news.com.au.
"It was a big house with a big backyard and you'd say it was a nice house. Old-fashioned styling, very 70s. It was a decent house in a normal street and it sounds like a cliche but it was a street just like any other.
"There was nothing in particular that stood out about the house except a big gate and a huge security system."
Clearly, Priklopil had something to hide inside. He let Kampusch, now 28, out of her dungeon only when his mother was not around. When she stopped by, he locked the young girl back up.
The dungeon was tiny, at the base of a set of stairs that led to bric-a-brac in Priklopil's garage. Behind a small cavity was a 5sqm room with a large concrete door.
Sadler said the thing that struck her most about Kampusch was how compassionate she was.
"When she was showing us around the house she kept asking if we were OK. She is hyper-intelligent, which helped her to survive and what is fascinating is she has a sort of sympathy for her kidnapper."
In an August interview, Kampusch admitted she carries a photo of Priklopil in her handbag. She may have sympathy for him, but she doesn't "know him", Sadler says.
"She spent 8.5 years with him but never spoke to him about anything. He never told her anything. She knows little about him."
After making her escape - Kampusch ran from her captor when he asked her to vacuum his car - one would expect her to never return.
But that's not the case. In fact, it's completely the opposite. Kampusch actually purchased the house she was kept in for all those years. She spends several nights a week there.
The reason? Sadler says it's about control.
"She wants to keep the house so it's not turned into a Disneyland for horror buffs," she said.
"She wants control for her life because she hasn't had control before."
Kampusch has written a book about her life titled Ten Years of Freedom. An investigation into Priklopil's death is still being looked into.