The family of Mohammed Makkawi Ibrahim, who was sentenced to death in the murder of the US diplomat John Granville and his Sudanese driver in 2008, received the news of his demise via an anonymous phone call which mentioned that he was killed during clashes between armed groups.
Ibrahim first came to the attention of Sudanese authorities in 2007 as a member of an extremist cell and was the head of the 4-man group that assassinated Granville.
Despite their arrest and conviction, the group managed to escape from maximum security Kober prison in Khartoum.
The US has offered $5 million for information on the escapees.
Ibrahim along with another convict, Mohannad Osman, managed to reach Somalia, and join the al-Qaeda affiliated al-Shabaab insurgents. Osman was reported killed in 2011.
An anonymous friend of Ibrahim said on an internet post that the 31-years old man was murdered after expressing desire to break away from al-Shabaab and join ISIS.
The post blasted al-Shabaab saying that "when the light of the caliphate emerged and the movement’s leadership refused to submit to the truth and reform its march, he [Ibrahim] showed his desire to join the Islamic State”.
“He never would have thought that al-Shabaab would sink to such a level of corruption".
He pointed out that the movement started persecuting Ibrahim and others who sought to join ISIS and began to imprison them.
Ibrahim was one of several who ran away “to the bushes” after the clampdown, the post said adding that al-Shabaab is going after those who were its main tenants.
An expert on Islamic extremist groups, al-Hadi Mohammed al-Amin, said that the incident indicates a serious escalation of conflict between al-Shabaab and ISIS in southern Somalia.
He told Sudan Tribune that the gap is widening between al-Shabaab and those seeking to pledge allegiance to ISIS.
Al-Amin noted that al-Shabaab refused to recognize ISIS and reaffirmed its allegiance to al-Qaeda leader Ayman al-Zawahiri.