Didn’t Jesus also say that:
John19:11 Jesus answered, Thou couldest have no power at all against me, except it were given thee from above: therefore he that delivered me unto thee hath the greater sin.
John19:12 And from thenceforth Pilate sought to release him: but the Jews cried out, saying, If thou let this man go, thou art not Caesar’s friend: whosoever maketh himself a king speaketh against Caesar.
From the cross Jesus asks forgiveness on behalf of those who do not know what they are doing.
It doesn’t mean Jesus is forgiving carte blanc, but that a particular group is being forgiven – those who do not have sufficient knowledge of their part in the crucifixion. It would also seem reasonable that the forgiveness is the granting of the possibilty (not the act itself) to become ratified upon repentance – which would happen for many at Pentecost when they realized what they did. The hideousness of directly putting Jesus, the actual son of God, to death is such that one might suppose it unforgivable altogether – Jesus is crying out to the father for pity.
It does appear that many people (the crowd) were involved without full knowledge of the error in their judgement. e.g. They did not know Jesus was innocent since their leaders stirred them up with charges against him. It is even possible that Caiphas really believed that Jesus was blaspheming. However, the problem is that envy was an alternate motive for the crucifixion before the erroneous belief of “blaphemy” came into play.
There were people, although I can’t judge (obviously) an individual case, who willed Jesus evil simply because he was Good. That is mortal sin in the crucifixion of Jesus.
And I think Petra is basically right, there were people who did not believe the charges but had a part in his crucifixion.