During the Black Death, Jews were thought to be responsible for the plague, and like many other occasions throughout the last few thousand years, they became victims of racial hatred. Many thousand were horribly tortured into giving false confessions (for poisoning wells) and executed; mostly by grotesque means such as burning, and in some cases, butchering.
These Jews, under torture, incriminated others. Records of their confessions were sent from one town to another in Switzerland and down the Rhine River into Germany, and as a result, thousands of Jews, in at least two hundred towns and hamlets, were butchered and burnt.
The sheer loss of numbers, the disappearance of their wealth, and the growing hatred of the Christians brought German Jewry to a catastrophic downfall. It now began to decline and did not again play an important part in German life till the seventeenth century.
The Black Death and the Jews 1348-1349 CE, Fordham University