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German police were investigating Wednesday after a woman was apparently kidnapped in the northern city of Hamburg and kept captive in a homemade torture chamber.

The Israeli woman made a brave escape from the soundproofed cell, made from a converted telephone booth, in 30-year-old Thomas Fischer's ground floor apartment -- fleeing when her captor forgot to lock the door and diving to freedom through a barbed wire-covered window.

The unnamed 26-year-old, an acquaintance of Fischer, was abducted at gunpoint Friday night from her home in Barmbek, a suburb of Hamburg -- 158 miles (255km) northwest of Berlin -- according to newspaper Hamburger Morgenpost.

Police fear Fisher was preparing for an extended stay with his victim, stocking his home with enough supplies to last him several months. But the woman said she fled to safety after just two-and-a-half hours, when he forgot to lock the chamber.

He is reported to have given chase, armed, but was unable to catch the woman, who ran to a friend's house where she alerted police.

When officers stormed Fisher's heavily fortified apartment, they allegedly found a pistol, a hand grenade and surgical equipment including a scalpel, syringes and gynecological tools with which he had experimented on a mannequin.

He had also stockpiled 113 fire extinguishers, some of which contained traces of explosives. In his bedroom were timber beams that police believe he had planned to use to board up the windows and doors.

Hamburger Morgenpost also reported that Fisher had been investigated previously for assault and stalking. He has not spoken since his arrest, according to reports, and no charges have been released.

A police spokesman was quoted as saying, "The whole two-roomed apartment was rigged up as one massive torture chamber, with this big old-fashioned telephone kiosk soundproofed as the cell for his victim."

The police prosecutor said, "It is evident that the apartment was meant as a place of confinement for some time."

Bild reported that police had begun searching for an accomplice who may have helped Fisher move the 276-pound (125kg), eight-foot-tall (2.3-metre-tall) phone booth and timber beams into his flat.

The case has drawn comparisons with that of Austrian woman Natascha Kampusch, who was held for more than eight years in a basement cell by Wolfgang Priklopil between 1998 and 2006.