I revealed my source, Gibbon's Decline and Fall. And I've found it online too for your convenience. Is is the precursor to the Crusades:
Chapter 57:The Decline And Fall Of The Roman Empire
You'll see how the Christians in Jerusalem were in fact granted their freedom of religion.
And here's the next chapter discussing the beginning of the first Crusade:
Chapter 58:The Decline And Fall Of The Roman Empire
You'll notice how the taste for war arose twenty years after the conquest of Jerusalem. Twenty years. Certainly the Turks were way out of line to have invaded in the first place, but seeing that any desire for war on the part of Rome came only 20 year later, we cannot reasonably conclude that it was just a continuation of a war started by the Arabs, but a separate war. If the Christians wanted Jerusalem, they should have fought back immediately, or if they were to wait, then at least have just cause such as the oppression of Christians.
Now the Arabs did murder many Christian in taking Jerusalem twenty years earlier, but seeing that that was no longer the case and that Christian pilgrims were free to visit and that local Christians had been granted their freedom of religion, any legitimate reason to attack at that stage no longer existed, thus we must conclude that Rome had started that war.
By the way, Gibbon is a well respected historian.