The male nurse dubbed Switzerland's "Angel of Death" has apparently confessed to killing a total of 27 patients.

Roger Andermatt admitted killing a further 18 elderly patients, it emerged yesterday, after saying this summer that he had killed nine.

Investigators said a nursing home employee had admitted putting his mostly women victims "out of their misery" by administering drug overdoses or smothering them with plastic bags and towels.

The 32-year-old was arrested in June after a suspicious death in a nursing home and subsequently admitted killing nine patients.

Sometimes he drugged them and blocked their noses and mouths until they stopped breathing, the investigating magistrate, Orvo Nieminen, told a press conference in Lucerne.

Mr Nieminen said Mr Andermatt claimed to have acted out of "sympathy, compassion, empathy, and salvation of the people involved".

"On the other hand, he also acknowledged that in several cases he had been overwhelmed by caring for the people involved. In some cases he felt relieved, somehow liberated, after the person had died."

The original nine killings came to light in May in a special unit for the senile in an elderly people's home in Lucerne, central Switzerland, where the nurse worked since December 2000.

The suspect, whom the authorities describe as well-educated, was arrested on June 28 and remains in custody.

Investigations were extended to other homes and hospitals where Mr Andermatt had worked. Five bodies have been exhumed.

Police traced 12 mercy killings to one home in the central Swiss canton of Obwalden, and said the rest happened in other homes or hospitals.

Mr Nieminen said the authorities wanted more information about what motivated the man to end the lives of people in his care. He was also to undergo psychiatric tests.

Euthanasia is tolerated in several Swiss cantons, provided strict rules are followed. The Swiss Exit organisation for voluntary euthanasia is also active in the Lucerne canton, helping terminally ill people who have decided to die.

Active euthanasia is banned in Switzerland but the country does not regard it as a crime for a doctor to assists suicide by prescribing lethal drugs which patients close to a painful death take themselves. The names of victims have not been released.

"The motives of the criminal are simply incomprehensible," the Obwalden canton government said. "The government regards it as tragic that such a crime could happen in such well-known and trusted surroundings." Special counselling has been set up for the victims' families and procedures at all state-run care institutions to prevent anything similar happening in future have now been reviewed.