In Nazi Germany, disabilities weren’t medical issues to be treated or solved—they were signs of racial inferiority. Hundreds of thousands of people with disabilities were imprisoned, experimented upon and murdered through a “euthanasia” program that preyed on the physically and mentally ill. The only traces of many victims were brain specimens that were collected for study after their death. And these specimens still exist today.

The samples of brain tissue will now be used to identify and acknowledge the victims, reports Brigitte Osterath for Deutsche Welle. In June, the Max Planck Society, whose scientific institutes are home to thousands of brain samples, slides and other materials relating to the victims, will fund and host a three-year research project to answer longstanding questions about the victims and the secretive Nazi program.

Known as Aktion T4, the project came out of Nazi ideology, which upheld a concept of racial purity and considered eugenics and "racial hygiene" a legitimate and acceptable field of scientific inquiry. Mental and physical disabilities were considered impurities that could be edited out of the Aryan gene pool, and programs and laws targeted at people with disabilities began as soon as Hitler took power in 1933.

In 1940, Aktion T4 began in earnest. As Brynnah McFarland writes for Rutgers University, the program consisted of death camps and “industrial” medical centers where people with disabilities were held, murdered and studied. Children and adults were given lethal injections, gassed and forcibly sterilized. It’s unclear how many people were ultimately murdered due to the secrecy of the program and the destruction of records.

During the war, the brains of hundreds of the victims were sent to Berlin to be reviewed at the Kaiser Wilhelm Institute for Brain Research. Though the organization was engaged in legitimate scientific research before the Nazis came to power, even winning multiple Nobel Prizes for advances in biology and cell research, it became a center for eugenics and “race science” and collaborated with Josef Mengele on horrific experiments at Auschwitz.

German research organization to identify Nazi victims that ended up as brain slides https://t.co/oqkY4WctYf pic.twitter.com/rar8wxnWbM — dwnews (@dwnews) May 3, 2017

At the end of the war, the Max Planck Society took over the institute and inherited its brain specimens. But they weren’t considered off-limits for researchers, Osterath reports. Scientists were free to use them in their research on disabilities, such as Down Syndrome, and many samples were used for decades after the war. Osterath notes that their provenance was kept hidden in scientific publications, which means it’s unclear how much current research is based on brain samples from murdered victims of the Third Reich.

In the 1980s, researchers discovered hundreds more of the samples. The society buried all of the known brain sections that dated from 1933 to 1945 in a Munich cemetery and erected a memorial to the victims in 1990.

The 1990s brought new revelations about the Max Planck Society itself and its involvement in Nazi-era crimes. As the institute notes on its website, this led to a historical commission, a public apology and publication of extensive research about the Kaiser Wilhelm Institute’s persecution of Jews and participation in atrocities. “The most honest form of apology is…exposing guilt,” the Society’s president said in a 2001 speech.

But that exposure wasn’t over yet. In 2015, even more brain sections were discovered inside the society’s archives. The society decided that it was time to learn as much as possible about the victims and to give their brain sections a proper burial. After an audit of the archive, the society determined it had found all of the specimens.

Now, it’s time to look into all of the specimens—including the earlier samples. In a press release, the society says it wants to figure out who they belonged to, how they were used, and to what extent Max Planck Society and Kaiser Wilhelm Society researchers were complicit. They’ll look at over 24,000 specimens with the help of an international research team.

The project won’t be cheap; according to the society, it will cost over $1.6 million and take three years. But it’s worth gathering more information about how the Nazis victimized their most vulnerable, more than 70 years after they were murdered.