St. Augustine, Sermon on the Monday After Easter (Sermon 229F):

"Many of those who said, 'His blood be upon us and upon our children,' later on came to believe the apostles bringing them the good news of the resurrection. His blood was indeed upon them, but it was to wash them, not to destroy them; well, upon some to destroy them, upon others to cleanse them; upon those to be destroyed, in justice; upon those to be cleansed, in mercy."