Jamieson, Fausset and Brown on Matthew 27:5

5. And he cast down the pieces of silver--The sarcastic, diabolical reply which he had got, in place of the sympathy which perhaps he expected, would deepen his remorse into an agony.

in the temple--the temple proper, commonly called "the sanctuary," or "the holy place," into which only the priests might enter. How is this to be explained? Perhaps he flung the money in after them. But thus were fulfilled the words of the prophet--"I cast them to the potter in the house of the Lord" (Zec 11:13).

and departed, and went and hanged himself--For the details, see on Ac 1:18.