GENEVA (AP) — Swiss prosecutors have dropped a criminal probe of the founder of the assisted suicide group Dignitas over urns containing human ashes that were thrown into Lake Zurich.

The Zurich prosecutors' office says an extensive investigation was unable to determine who tossed the urns into the lake. They were recovered in April.

In a statement on its website, the prosecutors' office said a probe against Dignitas founder Ludwig A. Minelli in connection with the urns was dropped July 28. Minelli declined Wednesday to comment on the decision.

Assisted suicide is legal in Switzerland but Dignitas has come under heavy scrutiny in recent years after critics and former employees have alleged unethical practices by the group.