The cramped, underground cell where an Austrian teenager was held captive for more than eight years might never have been discovered even if police had searched the house, an investigator said Sunday.

"Neither a normal house search nor a thermal imaging camera would have discovered this labyrinth," Maj. Gen. Gerhard Lang of Austria's Federal Criminal Investigations Bureau said in an interview with the newspaper Kurier.

Natascha Kampusch was kidnapped on her way to school in Vienna when she was 10. Her captor, Wolfgang Priklopil, largely confined her to the windowless cell in his home. He killed himself by jumping in front of a commuter train within hours of her escape on Aug. 23 that ended one of Austria's biggest police mysteries.

Lang described how, in order to get to Kampusch's cell, one had to go through a myriad of steps, including opening a vault with a code, removing bolts and crawling through a hole.

Police images released after Kampusch's escape showed the space contained, among other things, books, clothes, a television, a bed, a toilet and a sink.

Lang said he asked to be locked into the cell during the investigation.

"I could only take it in there for three minutes," he said.

Kampusch would not have survived had something happened to Priklopil, Lang added.

The Vienna public prosecutor's office announced on Nov. 17 that it had closed the Kampusch case, a day after police said they had completed their investigation.

The question of why Priklopil chose Kampusch as his kidnapping victim would "stay unanswered forever," Lang said.