Before 9/11, Imad Mughniyeh was responsible for killing more Americans than anyone else in the world. In 2008, after decades of being hunted, the senior Hezbollah figure was killed in a car bombing in Damascus that has since been attributed to a joint CIA-Mossad operation. A new SHOWTIME miniseries, “Ghosts of Beirut,” tracks Mughniyeh as he rose from the slums of Lebanon to become the most dangerous terrorist in the world, and explores how US and Israeli spies put their differences aside to work together in taking him down.