Describe European knights’ slaughter of Muslims and Jews during the First Crusade, and explain the Christian rationales for this slaughter

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1) Late in the year 1098, the Frankish army attacked the city of Ma’arra (present-day Ma’arrat an Nu’man in Syria). They killed thousands and took many prisoners and then committed further atrocities, according to Frankish chronicler Radulph of Caen, boiling adults alive, impaling children on spits, and eating them. In an official letter to the pope, the commanders explained that a famine made it necessary for the army to feed on Saracens. Descriptions of the slaughter of the Muslim citizens of Jerusalem, when the Crusaders finally took that city on July 15, 1099, are no less gruesome.
2) According to the Deeds of the Franks, a history written anonymously about 1100–1101, Count Emicho of Leiningen, making his way down the Rhine toward Jerusalem, robbed and murdered all the Jews he could find, killing 800 in Worms and wiping out the entire Jewish population of both Mainz and Cologne. Emicho seems to have been motivated by the need for funds to support his army, but his was a religious war as well. In his eyes, the Jews, like the Muslims, were the enemies of Christ.
3) Once Jerusalem was taken, Jews were burned alive or sold into slavery. The small number who survived did so by converting to Christianity.