Matthew 27: (New International Version)
24. When Pilate saw that he was getting nowhere, but that instead an uproar was starting, he took water and washed his hands in front of the crowd. “I am innocent of this man's blood,” he said. “It is your responsibility!”
25. All the people answered, “Let his blood be on us and on our children!”
http://bible.cc/matthew/27-25.htm
If you go to the link and scroll down to the commentary section, you will find several entries equating the subsequent suffering of the Jews with the crowd's utterance of the blood libel. And such views among Christians has been the source of a lot of mischief (and much worse) toward Jews over the centuries.
However, it should be noted that as early as the 13th century A.D., the Catholic Church's doctrine on the blood libel had shifted. If I understand the catechism correctly, it has been (and still is) the Church's position for a very long time that the Jews (and everybody else involved in the Crucifixion) lacked the actual power to kill Christ. He instead choose death willingly as a blemishless and perfect sacrifice for the expiation of Humanity's sins. Consequently, it is a libel (a false accusation) to assign ultimate responsibility to the Jews for Christ's Crucifixion.
It is in this, more nuanced, sense that Sarah Palin called the attribution of responsibility for the Tucson shootings last Saturday to the Right Wing a “blood libel.”
It would be later than the NT, obviously, and presumably somewhere in commentaries connecting, as you note, the exchange in Matthew with the persecution of the Jewish people.
But the term "blood libel" adds a second layer -- the determination that the accusation is false. That is why the date of origin of the term is significant, and should also give some clues as to when the term was applied to any false accusation of shedding innocent blood.