"Blood libel also called blood accusations, the superstitious accusations that Jews ritually sacrifice Christian children at Passover to obtain blood for unleavened bread ( matzot).
Blood libels were, unfortunately, common. When a body was found and the murder case could not be solved, the Jews were the usual suspects or scapegoats. No matter how much the Jews insisted that we are not allowed to consume even a drop of blood found in an egg, many gentiles spread the rumor that there was a secret ritual in which Jews use the blood of a Christian child to bake the Matzot. Historians have explained that these accusations gave the masses the excuse to persecute Jews, seeking their money, their power and positions. Probably the most famous blood libel in modern history was the "Damascus affair" in 1840 . When a Franciscan priest, Father Thomas, disappeared and the Jews were accused by the French, ignored by the British and tortured by the Turkish authorities of Damascus, with the intention to take the money and positions of the wealthiest families of the local Jewish community (see this).
In Aleppo, 1853, a blood libel was averted just on time. The body of a murdered gentile boy was planted in the house of Jewish baker at midnight. The plan was to come in the morning with the police and accuse the baker of a ritual murder. A Jewish baker was the perfect target to be charged. Jewish bakers "use Christian blood to knead matzot" and other ritual foods. Miraculously, the baker (named Moossa) woke up in the middle of that night. He discover the body, understood the potential accusation and got rid of it. When the authorities came they could not find anything. The baker informed the rabbis of the city of what had happened and they said that HaShem in His mercy saved the Jewish community of Aleppo from a terrible tragedy. They instituted that the 13 of Sivan be remembered as "Nes Moossan" (The miracle that happened thru Moossa) and Viduy should not be said on that day.
(There are other versions of this blood libel. As well as other explanation of why Viduy is not said this day: in the Diaspora, the six days after shabu'ot are finished the 13th of Sivan, not the 12th).
Incredibly, tyne accusations of BLOOD LIBELS did not go away. See for yourself!