A.T. Robertson Commentary Acts 5:22

"But the officers that came found them not in the prison; and they returned, and told," — Acts 5:22 (ASV)

The officers (ο υπηρετα). Under-rowers, literally (Matthew 5:25). The servants or officers who executed the orders of the Sanhedrin.

Shut (κεκλεισμενον). Perfect passive participle of κλειω. Shut tight.

Standing at the doors (εστωτας επ των θυρων). Graphic picture of the sentinels at the prison doors.