Charles Ellicott Commentary Ezra 5:17

"Now therefore, if it seem good to the king, let there be search made in the king`s treasure-house, which is there at Babylon, whether it be so, that a decree was made of Cyrus the king to build this house of God at Jerusalem; and let the king send his pleasure to us concerning this matter." — Ezra 5:17 (ASV)

Let a search be made. — All depended on the original decree, which nothing done in the meantime by the usurper could cancel. And the request of Tatnai seems to imply that it would be found: although the original was not found in Babylon, as was expected, a copy had been made.