A.T. Robertson Commentary Matthew 27:6

"And the chief priests took the pieces of silver, and said, It is not lawful to put them into the treasury, since it is the price of blood." — Matthew 27:6 (ASV)

Into the treasury (εις τον κορβαναν). Josephus (War II. 9,4) uses this very word for the sacred treasury. Korban is Aramaic for gift (δωρον) as is plain in Mr 7:11. The price of blood (blood-money) was pollution to the treasury (Deuteronomy 23:18f.). So they took the money out and used it for a secular purpose. The rabbis knew how to split hairs about Korban (Matthew 15:1–20), but they balk at this blood-money.