Swiss police have arrested several people after a controversial futuristic-looking capsule designed to allow its occupant to kill themself was used for the first time, authorities said on Tuesday.

Police in the northern canton of Schaffhausen bordering Germany said the so-called “Sarco” capsule had been deployed in a wood in the municipality of Merishausen on Monday.

Prosecutors in Schaffhausen have opened criminal proceedings against several people for “inducing and aiding and abetting suicide,” a police statement said, adding several people were detained, without giving details about them or the deceased.

A spokesperson for the group behind the capsule, The Last Resort, said the deceased was a 64-year-old American woman who had been suffering from a severely compromised immune system.

Florian Willet, co-president of The Last Resort, was among the four detainees, along with a Dutch journalist and two Swiss people, the spokesperson said. Willet was the only other person present when the woman ended her life, the spokesperson said.

In a statement issued by The Last Resort, Willet had described the death as “peaceful, fast and dignified.”