Americans were stunned on October 11 when the Justice Department unsealed its complaint against Mansour Arbabsiar, a 56-year-old used-car dealer from Corpus Christi now in federal custody, and Ali Gholam Shakuri, a member of the Iranian Revolutionary Guard Corps-Quds Force. Shakuri remains inside Iran. The pair have been charged with conspiring to kill the Saudi ambassador in Washington, Adel Al-Jubeir. As disclosed by the Treasury Department, the plot was coordinated by Arbabsiar’s cousin, Abdul Reza Shahlai, a top Quds Force functionary whom the Treasury designated in 2008 as one of several “individuals and entities fueling violence in Iraq.” Shahlai was...