Popper was one of the main perpetrators of the genocide against the native Selk'nam people[citation needed] in the islands,[2][3] and the circumstances surrounding his own death remain a mystery.

In 1886 he received a permit from the Argentine Government to form an exploration company to mine for gold near San Sebastián.

The expedition was rigorously and strictly enforced according to military standards with heavily armed men, with Popper in direct command of everything.

After the fight, Popper "posed his men in the attitude of troops repelling a charge, took a position himself astride one of the dead Indians, and then had the outfit photographed for subsequent use.

[10][11] In July 2022 The Wilhelm Filderman Center for the Study of the History of the Jews of Romania mounted in the Romanian capital, Bucharest, an exhibition of Popper's 1886 expedition into the interior of Tierra del Fuego.

It consisted of a selection of the hundreds of photographs of the expedition that Popper himself sent to his family in Bucharest at the time and which collection had previously been conserved in the Romanian National Archives.