Adam Clarke on Matthew 27:8

The field of blood - In vain do the wicked attempt to conceal themselves; God makes them instrumental in discovering their own wickedness. Judas, by returning the money, and the priests, by laying it out, raise to themselves an eternal monument - the one of his treachery, the others of their perfidiousness, and both of the innocence of Jesus Christ. As, long as the Jewish polity continued, it might be said, "This is the field that was bought from the potter with the money which Judas got from the high priests for betraying his Master; which he, in deep compunction of spirit, brought back to them, and they bought this ground for a burial-place for strangers: for as it was the price of the blood of an innocent man, they did not think proper to let it rest in the treasury of the temple where the traitor had thrown it, who afterwards, in despair, went and hanged himself." What a standing proof must this have been of the innocence of Christ, and of their perfidy!