The Last Resort, creators of the Sarco suicide pod, confirmed a 64-year-old Midwestern woman died Monday using its device -- noting the company's co-president Florian Willet was the only other person present, despite a contrary report from the police.

Local police in Northern Switzerland have confirmed multiple people were detained after the death -- the first using the Sarco pod -- with prosecutors opening an investigation into suspicion of incitement and accessory to suicide.

In Switzerland, assisted suicide has been legal since the '40s ... giving the European country a reputation for "suicide tourism."

The suicide pod -- which was reportedly located beneath a canopy of trees for the woman's death -- injects a sealed chamber with nitrogen gas, allowing the user to fall asleep before suffocating to death moments later.

It's important to note there's said to be a button located inside the pod, which gives the user control on whether the gas is injected ... a crucial part of the design considering Swiss law requires the person dying to trigger the suicide.

The U.S. woman, who passed away on Monday, had reportedly wanted to die for the last 2 years ... given she had suffered from "a very serious illness that involves severe pain."

Last Resort expressed a similar sentiment, noting the woman -- who has yet to be identified -- had suffered for "a number of years" following a battle with "severe immune compromise."

Last Resort member Fiona Stewart claims the company was acting on the advice of their lawyers ... and Willet says the woman's death was "peaceful, fast and dignified."

A legal firm reportedly tipped off the police about the use of the pod in an assisted suicide, which prompted the investigation ... though, Last Resort noted it expected this would happen in the aftermath of its launch.