In 16's files in Assassin's Creed 2 it indicates that Jeanne d'Arc was killed because she had the Piece of Eden: Sword.
I am unsure if the Templars knew that Jeanne d'Arc had a Piece of Eden so I am wondering, did the Templars manipulate events to see her killed for the sole purpose of getting the Sword or did someone see what the Sword did and believed it was witchcraft and the Templars only learned the Sword was a Piece of Eden after her death.
Best Answer
According to this unofficial wiki:
Since the Templars apparently orchestrated her execution, it is very likely they already knew about the Sword beforehand.