Several neuropathologists conducted brain research on victims of so-called euthanasia programs carried out by the National Socialist (Nazi) regime in Germany from 1940 to 1945. Some published their results in German journals or books during and after the war. One of these neuropathologists was Hans Jacob of Hamburg, a former Nazi party member and the leader of the same laboratory previously run by Alfons Jakob (Creutzfeldt-Jakob disease). Though much has been published on the unethical actions of Jacob's fellow neuropathologist from Berlin, Julius Hallervorden, Jacob's actions were remarkably similar and have not been previously analyzed in the neuroscience literature. Jacob dissected at least 42 patient brains from euthanasia centers near Hamburg, and saved the specimens from at least 17 of them. He published a 1956 book chapter featuring 2 such specimens. Jacob was denazified, had a notable career, and never publicly addressed his actions during the war. His ethical violations may not have been on the same scale as Hallervorden’s, but the effect of his work echoes to the modern era. As responsible researchers, we must always be conscious of the provenance of material provided and not succumb to opportunistic temptation despite the ethical consequences.