The alleged mastermind of the terrorist attack in Garissa that left 147 people dead is a Kenyan national, illustrating how national boundaries have become blurred in the country’s war with Somalia-based Islamist militant group al-Shabaab.

Mohamed Mohamud aka Dulyadeyn, believed to be a close friend of al-Shabaab’s leader, Ahmed Omar Abu Ubeyd, is now the subject of a bounty of 20m shillings (£145,000) for his suspected role in organising the attack.

He has several aliases, including Gamadhere, Kuno and Abdurahman, according to a Somali security source, and is thought to be responsible for leading al-Shabaab’s operations in Kenya. Dulyadeyn, who is in his mid-40s and has three wives, was linked to the audacious attack on the Westgate shopping mall in Nairobi and was recently accused of orchestrating 12 militants in a plot against the Kenyan parliament.

His career began conventionally enough as an engineer who earned a degree from Jomo Kenyatta University in Nairobi in the early 1990s. He worked for the Saudi-based al-Haramain Islamic Foundation, according to Kenya’s Star newspaper, and was then a teacher and principal of a madrasa, or Islamic school, in Garissa.

But he became increasingly radicalised and crossed the border into Somalia, joining the Islamic Courts Union. After that movement collapsed, he held a variety of positions in al-Shabaab. He is alleged to have been behind several attacks on Kenyan troops who are fighting the militant group in the Jubaland region.

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