This I know for a fact is not true. I have read a great deal about the Hundred Years War and the rule was kill all but the knights who might pay ransom. Since I posted to you I have checked 3 on line encyclopedia sources about the First Crusade and they all agree that there was a massacre of some size and that it was common practice in that day.
You can read the sources for yourself here (in English):
http://www.fordham.edu/halsall/sbook1k.html