The broad shoulders of male nurse Stephan Letter, Germany’s Angel of Death, quivered today as he was sentenced to life imprisonment for killing 28 patients, making him the country’s worst serial killer since the war.

It marked the end of a nine-month trial that has stunned the sleepy mountain community of Sonthofen which was pronounced "The Alpine Town of 2005".

Choking back tears the milky-faced 28-year-old turned first to his lawyer - who had presented him as a mercy killer tormented by the suffering of others - and then to the public gallery where relatives of the dead had come to see justice done. He seemed to mouth four short words in their direction: "Es Tut Mir Leid" - I’m sorry.

Judge Harry Rechner, found Mr Letter guilty of murder in 12 cases, manslaughter in 15 and killing on demand in another as well as attempted manslaughter and causing grievous bodily harm.

In a highly unusual decision for Germany, he ruled that no upper limit should be placed on the life sentence, ensuring that Mr Letter could not be released after 15 years for good behaviour.

When doctors first suspected that Mr Letter had been fatally injecting patients with a cocktail of tranquilisers and muscle relaxants in 2004, a massive process of exhumation began. Bewildered tourists would pass forensic scientists in white hooded overalls on their way to dig up corpses: over 40 bodies were examined, all patients who had died during Mr Letter’s shifts.

Waltraud Schoenberger, a 55-year-old mother of two was one of those who welcomed the sentence. Her 79-year-old mother Beata Giehl was taken to the Sonthofen Clinic on April 30, 2003 with a suspected heart attack. By late afternoon however Mrs Giehl was chatting cheerfully with her daughters. By 10 o’clock that evening she was dead.

"I hope that this murderer stays in prison to the very end of his life," said Mrs Schoenberger. "Sure, he had a difficult childhood but it can’t be that everyone like that becomes a killer."

Cases such as that of Mrs Giehl were crucial to the final sentencing. They exposed the weakness of Mr Letter’s mercy-killing defence. Many of the patients that he fatally injected on his night shift were recent admissions and even the doctors had not had a chance to make a definitive diagnosis.

Mr Letter had claimed he was relieving excruciating pain or responding to pleas for a quick death. Yet trial testimony showed again and again that this was not plausible. His last victim, a 73-year-old Spanish woman, Pilar Del Rio Peinador, had been admitted to hospital with breathing problems but was already well enough to be planning a holiday in her homeland when she was fatally injected in July 2004.

Defence lawyer Juergen Fischer had presented Mr Letter as a complex, disturbed man. Mr Letter’s coordination had been poor as a child and his plainly disturbed mother had become convinced that he was mentally handicapped: over a period of several years she took him from one doctor to another.

His first ambition was to be a casualty doctor but mediocre school marks meant that he had to settle for nursing. At one hospital he fell in love with a female nurse who was suffering from a borderline personality disorder. Mr Fischer who had ordered a psychological examination of the young woman - to show how a crime could evolve from a relationship between two psychologically damaged people - said he was disappointed that the judge had not taken into account all the mitigating circumstances. His client is considering an appeal.

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