To secure himself against danger from Aristobulus, Herod instituted a system of espionage against him and his mother. This surveillance proved so onerous that they sought to gain their freedom by taking refuge with Cleopatra. Their plans were betrayed, however, and the disclosure had the effect of greatly increasing Herod's suspicions against his brother-in-law. As he dared not resort to open violence, he caused him to be drowned while he was bathing in Jericho.