Assassins and Al Nusra front both are Islamic fundamentalist groups and their purpose is purification and fulfillment of Islamic teachings. The goal of both parties has a political base behind it. Assassins threaten the Seljuk Empire in Syria and Persia whereas Al Nusra front aims at ending the regime of Basher Al Assad in take hold of Syria and Lebanon.
As they both belief that they are purifying the religion, they are phonetics and do not fear death. They also do not experience guilt or remorse for what they do.
A public community is required by both of them for their act and hence their act is not at all hidden. Assassination used to occur in Royal Courts in presence of public and Al Nusra also cause killing in the public in the form of suicide bombing at cars, schools and other parts of community etc.
Moreover both of these do not run away and may die for the religion. This is regarded as an honorable rank of martyrdom. Assassins fight and die showing their devotion and similarly Al Nusra also confronts and even claims the responsibility for their acts.
Method to kill varies between the two groups as ritually significant dagger for assassins and explosive devices as bombs and snipers for Al Nusra front.
Both of these provide training to selected individuals but assassins lives in apprenticeship and learns to assassinate but Al Nusra provide training to individuals who are willing to join them and they are recommended by ay of the existing member. They were vocal and hand missionaries and consultative leaders to guide them.
To summarize both of these are very much interrelated as both focus on social transformation and religious purification.