So far I have identified two ex-Guantánamo detainees of Moroccan origin fighting in Syria under the banner of Harakat Sham al-Islam: namely, Abu Hamza al-Maghrebi (Mohammed al-'Alami) and Abu Ahmad al-Muhajir (Ibrahim bin Shakaran). The latter is the leader of Harakat Sham al-Islam: a Moroccan-led mujahideen group operating primarily in Latakia and Aleppo governorates. The group recently played a role in the capture of al-Kindi hospital from regime forces alongside Jabhat al-Nusra and the Islamic Front.
Now I have identified another Moroccan ex-Guantanamo detainee: Mohammed Mizouz, going under the alias of Abu al-Izz al-Muhajir. He appeared only many hours ago in a video where he makes a speech on the necessity for the unity of the mujahideen, appearing alongside fighters from both Islamic State of Iraq and ash-Sham and Jabhat al-Nusra in Latakia.
Figure 2: Screenshot of video of Abu al-Izz al-Muhajir's speech. He is in the center under the Harakat Sham al-Islam flag with the Qur'an directly in front of him.
Besides being informed of the identity of Abu al-Izz al-Muhajir with Mohammed Mizouz by a Moroccan jihadi supporter, one should also note that we have other attestations to his appearance. Indeed, the identity is unmistakable.
Figure 3: Video of Mohammed Mizouz in March 2012 in Rabat, Morocco.
You can read more about Mohammed Mizouz here. Originally from Casablanca, he was transferred to Morocco after being released from Guantánamo on no charges.