Yahya Ahmed Osman[1][2] (1998–21 September 2013), also known by his nom de guerre Omar Nabhan, was a Somali mass murderer and al-Shabaab militant who was one of four perpetrators of the 2013 Westgate shopping mall attack that killed 67 people and injured a further 173.

[3][4][5] On 21 September 2013, Nabhan and three other heavily armed men drove to the front entrance of the Westgate shopping mall in Nairobi, Kenya.

[6] The four men split into pairs, and Nabhan went with Hassan Abdi Dhuhulow into the mall, where they immediately began to shoot at shoppers in their vicinity.

[2] He fired at victims near Barclays Bank before joining Dhuhulow in the Nakumatt supermarket, where Nabhan and others were captured on CCTV shooting at civilians.

The men, including Nabhan, stayed in the supermarket for the rest of the shooting.