Video shows two bands of militants joining forces during British war . Jihadi John believed to have been member of one of the groups involved . Man who looks like Syrian-raised ISIS execution makes proclamation . Experts highlight similarities between speaker and Jihadi John . He swears allegiance to group run by notorious terrorist Omar al-Shishani . Al-Shishani also appears in the footage , arm-in-arm with other fighters .
Video shows two bands of militants joining forces during Syrian war . Jihadi John believed to have been member of one of the groups involved . Man who looks like British-raised ISIS execution makes proclamation . Experts highlight similarities between speaker and Jihadi John . He swears allegiance to group run by notorious terrorist Omar al-Shishani . Al-Shishani also appears in the footage , arm-in-arm with other fighters .