They Know Not What They Do?
Apparently, many people assume that Jesus asked forgiveness for his executioners because those poor slobs thought they were torturing an ordinary guy to death, which is then believed to be less horrid than killing the Son of God.
But in the Old Testament (which, covenantally spoken, ends at the resurrection and not the birth of Christ) we find the Mosaic law of an eye for an eye (and a death for a death).
Jesus was not asking forgiveness for their act, because that act was ordained pretty much at the creation. In stead He was asking forgiveness for their ignorance ("...for they know not what they are doing". Not knowing that Jesus was the Christ—who had to be brought to death—was their transgression.