A researcher has discovered the 70-year-old remains of Jewish victims of Holocaust-era gas chambers at a medical research facility in Strasbourg, France.

Along with tissue samples, Raphael Toledano found a 1952 letter by the director of the Strasbourg Medical Institute, Camille Simonin, that discussed experiments that were conducted on the tissues by Nazi anatomist August Hirt. The tissue samples themselves were found in test tubes and a jar that were stored in the institute’s closed collection.

“It was a shock to discover that these jars were still there, that we put in a museum display a part of these Jews who were murdered by the Nazis,” Toledano said, adding that the jar contained skin fragments and that the test tubes contained tissue samples from intestines and a stomach, the Associated Press reported.

“The labels identify each piece with precision and mention the register 107969, which matches the number tattooed at the Auschwitz camp on the forearm of Menachem Taffel, one of the 86 victims,” Simonin wrote in the letter, which identified the samples.

Jewish communities in Europe have since questioned how long authorities knew about the existence of these tissue samples.

“This discovery raises serious questions about who knew about these remains and why they did not reveal this sooner,” said a spokesman from the Board of Deputies of British Jews.

Currently, the Strasbourg mayor’s office plans to return the remains to the city’s Jewish community for burial.