According to Beha Ed-Din, a muslim chronicler, Richard the Lionheart pretty much broke the medieval equivalent of the Geneva Convention and slaughtered a huge number of captives during his crusade in outremer.
This was the Third Crusade in response to Saladin’s successful conquest of all the major cities of the kingdom of Jerusalem including the holy city itself. A determined Richard appeared on the scene and took Acre back. In the process, he got hold of just under three thousand captives.
The ransom for sparing their lives was 200,000 gold pieces, 1500 crusaders to be released and the return of the Lignum Crucis – the True Cross. Various wrangles then ensued between the two days and losing his patience, Richard decided to make his intentions very plain to the Saracens. He gave the order for, essentially, mass murder.
As the chronicler explained:
The Franks then flung themselves upon them all at once and massacred them with sword and lance in cold blood. Our advanced guard had already told the Sultan of the enemy’s movements and he sent it some reinforcements, but only after the massacre. The Muslims, seeing what was being done to the prisoners, rushed against the Franks and in the combat, which lasted till nightfall, several were slain and wounded on either side. On the morrow morning our people gathered at the spot and found the Muslims stretched out upon the ground as martyrs for the faith. They even recognised some of the dead, and the sight was a great affliction to them. The enemy had only spared the prisoners of note and such as were strong enough to work.