 According to "Al Arabiya", while serving 13 years in prison, he left Fatah and joined Hamas after meeting with some of the latter's founders who were also incarcerated at the time, namely Abd al-Aziz Rantissi, Nizar Rayyan and Salah Shehadeh.After his release, in 1995 Jabari began to act as a commander in the military wing of the Hamas.In addition, he dealt with the movement's charitable organizations and was responsible for coordinating between the collection of money and military activities.