Albert Barnes 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 there be search made ... at Babylon - They perhaps doubted whether proof of the decree of Cyrus remained in the archives. The Pseudo-Smerdis had had the records in his power for seven months; and, when he reversed the policy of his predecessors, might have been expected to destroy their edicts. The decree was not found at Babylon, the most natural place for it, but in the provincial capital of Ecbatana, which Tatnai and his friends had not asked Darius to have searched .