They included Midhat Mursi al-Sayid Umar , who the U.S. Justice Department called an explosives and poisons expert ; Abu Obaidah al-Masri , the al-Qaida chief responsible for attacks on U.S. forces in eastern Afghanistan ; and Abdul Rehman al-Maghribi , a Moroccan and relative of al-Zawahri , possibly his son-in-law .