there was a similiar case in germany a few years ago
the policeman who threatened the murderer with torture to save the life of the kidnapped child, was accused in court because of it and lost.
"Kidnapping Has Germans Debating Police Torture
By RICHARD BERNSTEIN
Published: April 10, 2003
The two most important facts of the case were readily accepted today by the prosecution and the defense as the trial of a 27-year-old law student named Magnus Gäfgen opened in a standing-room-only courtroom here.
The first fact is this: on Sept. 27, Mr. Gäfgen kidnapped Jakob von Metzler, the 11-year-old son of a prominent banker, and murdered him by wrapping his mouth and nose in duct tape.
Four days later, Mr. Gäfgen was arrested after the police watched him picking up the ransom, but after hours of interrogation he was still refusing to disclose where Jakob was being kept.
That is what produced the second undisputed fact: imagining that Jakob's life might be in imminent danger, the deputy police chief of Frankfurt, Wolfgang Daschner, ordered subordinates to extract the necessary information from Mr. Gäfgen by threatening to torture him.
Mr. Gäfgen was told, his lawyer later said, that ''a specialist'' was being flown to Frankfurt by helicopter and that he would ''inflict pain on me of the sort I had never before experienced.''"
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link to www.nytimes.com]