He led a "reign of terror" after the fall of Timbuktu to the Ansar Dine group in 2012. The International Criminal Court (ICC) imposed a 10-year prison sentence on al-Hassan ag Abdoul Aziz ag Mohamed ag Mahmoud, the former head of the Islamic police in Mali’s historic Timbuktu, for war crimes committed during this tumultuous period. Prosecutors described his leadership as a period of extreme oppression marked by torture, public amputations, and brutal punishment of local civilians, including children.

In June 2023, the ICC found him guilty of specific abuses, while he was acquitted of charges related to rape, sexual slavery, and the destruction of Timbuktu's revered ancient mausoleums. His extradition to the ICC occurred in 2018, following a French-led military intervention that liberated Timbuktu from jihadist control five years earlier.

The Islamist group Ansar Dine capitalized on an ethnic Tuareg uprising to seize control of northern Mali cities, where several other militant leaders—like Ahmad al-Faqi al-Mahdi, who admitted to destroying significant cultural sites—have been prosecuted. Timbuktu, renowned as a historical center of Islamic scholarship and culture from the 13th to 17th centuries, gained UNESCO World Heritage status in 1988, underscoring the importance of preserving its rich heritage in the face of ongoing threats.

This sentencing serves as a reminder of the atrocities committed under the rule of extremist groups in the region, focusing attention on the ICC's role in addressing international crimes and providing justice for the victims.