Advocacy groups behind a so-called suicide capsule said Sunday they have suspended the process of taking applications to use it — which numbered over 370 last month — as a criminal investigation into its first use in Switzerland is completed.

The president of Switzerland-based The Last Resort, Florian Willet, is being held in pretrial detention, said the group and Exit International, an affiliate founded in Australia over a quarter century ago.

Swiss police arrested Willet and several other people following the death of an unidentified 64-year-old woman from the U.S. Midwest who on Sept. 23 became the first person to use the device, known as the “Sarco,”in a forest in the northern Schaffhausen region near the German border.

Others initially detained were released from custody, authorities have said.

___ EDITOR’S NOTE — This story includes discussion of suicide. If you or someone you know needs help, the national suicide and crisis lifeline in the U.S. is available by calling or texting 988. There is also an online chat at 988lifeline.org. The Swiss government refers queries about suicide prevention to a group called “Dargebotene Hand,” or The Offered Hand. ___

Switzerland has some of the most permissive laws in the world when it comes to assisted suicide, though the first use of the “Sarco” has prompted a debate among lawmakers.

Laws in the rich Alpine country permit assisted suicide so long as the person takes his or her life with no “external assistance” and those who help the person die do not do so for “any self-serving motive.”

The advocacy groups said in a statement Sunday that 371 people were “in the process of applying” to use the Sarco in Switzerland as of Sept. 23 and applications were suspended after its first use.

Exit International, whose founder Dr. Philip Nitschke is based in the Netherlands, is behind the 3D-printed device that cost over $1 million to develop.

The “Sarco” capsule is designed to allow a person sitting in a reclining seat inside to push a button that injects nitrogen gas into the sealed chamber, allowing the person to fall asleep and die by suffocation in a few minutes.

Exit International has said Willet was the only person present during the woman's death, and described it as “peaceful, fast and dignified.” Those claims could not be independently verified.