In 2013, a letter and an audio recording of Ayman al-Zawahiri, the leader of al-Qaeda, was leaked to Al Jazeera. In it, al-Zawahiri disbanded the Syrian faction of ISIL. The group's leader, Abu Bakr al-Baghdadi, opposed this ruling on the basis of Islamic law. The group has since continued to operate in Syria. Starting in April 2013, it made rapid military gains in large parts of Northern Syria, where the Syrian Observatory for Human Rights described them as "the strongest group". They have sought publicity by releasing videos of the decapitation (beheading) of journalists and other prisoners of war mainly done by member Jihadi John. He was killed in November 2015.