Advocacy groups behind a "suicide capsule" announced Sunday they have suspended applications to use the device until authorities in Switzerland complete a criminal investigation into a woman's voluntary death from its first use.

The president of Switzerland-based The Last Resort, Florian Willet, is being held in pretrial detention, according to the group and Exit International, an affiliate founded in Australia. Both organizations advocate for the right to assisted suicide.

Swiss police arrested Willet and several other people following the death of a 64-year-old American woman who last month became the first person to use the device to voluntarily end her life, according to The Associated Press. The device, known as the "Sarco," was used in a forest in the northern Schaffhausen region of Switzerland near the German border on Sept. 23.

Other people who were initially detained in connection with the woman's death were released from custody, according to authorities.

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The woman was reportedly suffering from severe immune compromise.

Assisted suicide is legal in Switzerland, with laws allowing so-called death with dignity as long as the person ends their life with no "external assistance" and people who assist the person 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, but that applications were suspended after its first use.

Exit International, whose founder Philip Nitschke is based in the Netherlands, is behind the device, which was 3D-printed and cost more than $1 million to develop.

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The capsule was designed to allow a person to sit in a reclining seat inside the device and push a button that injects nitrogen gas from a tank underneath into the sealed chamber. The person would then fall asleep and die by suffocation in a few minutes.

Exit International has said Willet was the only person present for the woman's death, which the group described as "peaceful, fast and dignified."

On the day of the woman's death, Swiss Health Minister Elisabeth Baume-Schneider told parliament that use of the device would not be legal.

But Exit International pushed back on Baume-Schneider's statement, arguing that the group's lawyers in Switzerland believe use of the device is legal.

"Only after the Sarco was used was it learned that Ms. Baume-Schneider had addressed the issue," the advocacy groups said in the statement Sunday. "The timing was a pure coincidence and not our intention."

The Associated Press contributed to this report.