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GENEVA (AP) — Swiss authorities are investigating a macabre discovery: Dozens of urns filled with human ashes stuck in the mud beneath Lake Zurich.

The surprise find — by divers searching for their boat's lost sunroof — is drawing attention to some uncomfortable aspects of assisted suicide, a practice permitted in Switzerland but which is coming under increasing public scrutiny.

Zurich police won't say if they have evidence directly connecting the rust-colored urns to Dignitas, a Swiss group that has helped hundreds of people — including Americans, Britons, Germans and Frenchmen — take their lives in recent years.

"That would be pure speculation," said Wolfgang Bollack, spokesman for Zurich's environmental department.

But The Atlantic, a magazine in the United States, just reported eerily similar burials conducted by Dignitas founder Ludwig Minelli. In a profile of him last month, the magazine said that Minelli stores the urns until he has enough to fill up his car then dumps them at night into Lake Zurich from a "quiet spot nestled among the multimillion-dollar houses."

Soraya Wernli, a former Dignitas employee, recounted a similar story in 2008 from her time with the organization. She described dumping urns into the lake as a common practice and said hundreds were under the water.

Minelli said "they would dissolve in the water, that they were urns made of tons of clay," Wernli recently told television channel TeleZueri.

Attempts to reach Minelli and Wernli were unsuccessful Wednesday and Dignitas declined to answer questions from The Associated Press.

Minelli, a bespectacled Swiss lawyer, has helped turn Zurich into a suicide capital with his crusader's zeal for the right of "dignity in death," and the group helps over 100 people each year to kill themselves.

Critics, however, contend that Dignitas is a profit-turning organization that operates on the fringe of medical ethics and public opinion.

The word "Sterbetourismus" — suicide tourism — was named word of the year in Switzerland in 2007 and still provokes intense debates.

The police probe began last week after the muddy, encrusted urns were discovered accidentally by divers near Zurich's extravagantly wealthy "Gold Coast" only 5 miles (8 kilometers) from the city center. That northeastern side of the lake — which sinks to a depth of over 440 feet (136 meters) — has multimillion-dollar estates, marinas and lush public parks along its shores.

The divers brought 13 of the ash containers out of the water and called the Zurich police, who later hauled away another 22 urns in an effort to deter "diving tourism." Others are believed to remain under water and police have stopped trying to pull any more out.

"We're trying to determine how the urns got into the lake," said police spokesman Stefan Oberli.

Zurich authorities say the lake urns poses no public health concern, as the ashes were too few to damage the important drinking reservoir or disturb popular summer swimming sites.

But the disposals are illegal without a permit. The investigation involves illegal lake burials and the more serious crime of disturbing the sanctity of the dead. The second offense is punishable by up to three years of prison, but would more likely result in a fine.

Bollack said authorities received complaints in 2008 of someone spreading ashes in Lake Zurich, and Dignitas was suspected at the time.

"We couldn't prove it, we had no evidence, but we sent a letter to Dignitas to remind them of the law," Bollack said.

Beyond criminal consequences, the urns episode could prove far more serious for Dignitas' image as it battles to maintain public support. Critics have questioned the group's use of helium in suicides and claim that some patients elected death even when they weren't terminally ill. Local property owners, meanwhile, have complained each time Dignitas that has moved.

Switzerland lives and breathes for tourism — but death tourism is not a subject any official wants to talk about.

Zurich authorities have forced Dignitas to relocate numerous times in recent years. At one point, the group operated out of a mobile home and at another time from a hotel room — a far cry from the image of a sanitized Alpine clinic that the group tries to portray.

While most Swiss are fiercely independent and want the option of assisted suicide for themselves and family members, the government last year proposed to restrict or even ban Dignitas and others to cut down on suicide tourism from abroad.

The new rules would require assisted suicide groups to exhaustively document their contact with patients. Patients, meanwhile, would need two medical opinions showing that their illness is incurable and likely fatal within months, and that they are fully mentally capable of deciding whether to end their lives.

Some are theorizing that the urns and the ashes could be related to foreigners, who were either unwilling or unable to transport them back home. Bringing ashes onto a civil airplane is a complicated procedure that requires various forms of documentation.

The Zurich crematorium wouldn't say if foreigners not residing in Switzerland could have their ashes deposed in its vault.

Burials are sometimes permissible in the lake, but must be authorized.

"We can accept these in individual cases, for example when a man who lived his whole life on Lake Zurich wants to be put to rest in the lake," Bollack said. "We certainly wouldn't tolerate so many."

As for the crime of disturbing the dead, Bollack said it would be up to a magistrate to decide whether there were grounds to press charges.

"We assume that this isn't a reflective burial when so many are thrown into the lake," he said.

Authorities haven't decided what to do with the ashes they've recovered. The urns aren't named, making it difficult to give the dead a second burial in a public cemetery.

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AP writer Eliane Engeler contributed to this report.