- Senior political leader of Hamas
- Founder of the Holy Land Foundation for Relief and Development
A senior political leader of Hamas, Marzook is responsible for the deaths of numerous Israelis. In 1981 he founded the Islamic Association for Palestine (IAP), widely regarded as the "primary voice in the United States" of the terrorist group Hamas. He is also the founder of the Holy Land Foundation for Relief and Development, an organization whose assets were blocked by the United States government for funneling money to Hamas. And he is the founding President of the United Association for Studies and Research (UASR), a prominent Islamist think tank related to Hamas. In 1997, Marzook was extradited by the United States to Jordan. From there he went to Syria, where he currently serves as the Deputy Chief of Hamas' Political Bureau.
In the summer 2007 Holy Land Foundation for Relief and Development (HLF) trial (which looked into evidence of HLF's fundraising on behalf of Hamas), the U.S. government released a list of approximately 300 of HLF's "unindicted co-conspirators" and "joint venturers." Among the unindicted co-conspirators were many individuals affiliated with the Muslim Brotherhood and/or Hamas, including Mousa Abu Marzook, Omar Ahmad, Abdurahman Alamoudi, Yousef al-Qaradawi, Abdallah Azzam, Jamal Badawi, Mohammad Jaghlit, Abdel Aziz Rantisi, and Ahmed Yassin. The list also included groups such as the Council on American-Islamic Relations, Hamas, INFOCOM, the Islamic Association for Palestine, the Islamic Society of North America, the Muslim Arab Youth Association, the United Association for Studies and Research, and the North American Islamic Trust.