You'll notice he spoke in the present tense, my friend.
First off, the crusades are maybe not your best example, seeing as they were targeted more at the Muslims who actually controlled the lands in question and deaths of Jews were incidental. But, to answer your question anyway, most of the people we are talking were completely illiterate and could not read one word of the Bible on their own. That makes following all the handy-dandy instructions inside a little difficult, especially with corrupt rulers who fit reason to their personal ends and not vice versa.
Crusades? Before you claim the Crusaders murdered Jews you need a little history lesson. There were many Crusades, eight in all I believe. Some European Jews were killed by a wild, unruly gang of Christians during an unsanctioned, unorganized "people's crusade" that occurred before the first military Crusade into Islam. This unruly mob included many criminals, drunkards, and mostly low brow types with no military plan, only a handful of Knights amongst their leadership and no rule of law. They included men, women and children, and they were "armed" with clubs, pitch forks and axes. When they finally arrived in Islam they were butchered instantly, tens of thousands of them, and this mob of criminals received thier just deserts.
The first real military Crusade took place a short time later, when an estimated 500,000 trained Knights, cavalry and foot soldiers left to protect Western Europe from imminent Islamic invasion. (Islam had just crushed the entire Greek Army 20 years earlier at Manzikert, and had nothing to stop them now from entering Western Europe with their hordes of crazed horsemen).
By the time these weary, depleted and utterly battered Crusaders finally reached Jerusalem there were only about 15,000 left of the original 1/2 million men. They suffered horrendous losses by enemy attack, starvation and thirst, sickness and the severe elements. At Jerusalem they found the city heavily fortified with tens of thousands of Mohammedan soldiers.
Included in these forces were another small army of huge Black soldiers, mercinaries imported from Africa to help slaughter the Crusaders. After several frantic attempts to scale the walls to take the city failed, and the Crusaders took yet more horrendous losses, they regrouped outside the walls of Jerusalem overnight and prepared for another assault. This final assault they knew could not fail, or else they would be destroyed. Any survivors would have to return to Europe in defeat.
After marching for thousands of miles in enemy territory, and suffering unspeakable losses, these relatively few remaining Crusaders were in a savage mental state. Do or die. Kill or be killed. They attacked once more, this time in a feverous battle pitch that literally horrified the city's defenders. They scaled the walls and fought like demons, killing anyone and anything in front of them. The Mohammedans and the huge, muscular Black defenders fell like flies. The Crusaders penetrated the city's defenses and went from building to building to slaughter whomever they saw. There was no retreat, no stopping to think or to rest. It was a route, and indeed became a slaughter. It is well recorded that the Crusader's leaders tried vainly to prevent the killing of civilians and innocents. But the loss of 97% of their men in battle, or to sickness, the months and months of marching through rugged, hostile, trecherous land, all these events put the surviving Crusaders into a brutal battle state and there was no stopping them in their final assault.
Yes, Jews died on this day, but to claim it was planned, or was done with forethought and malice, to call them murderers is not quite true. Once you know all the circumstances then you understand that it's unfair to claim their intention was to murder Jews.
It is historical fact that centuries later many Jews fought side by side with the Mohammedans when they conquered Christian Spain, and helped them to suppress Christianity. Perhaps you care to explain this, since you have decided to talk about ancient history.