CNN - The Army Psychiatrist who killed 13 people at Fort Hood is asking to join ISIS from his federal prison cell. Nidal Hasan's attorney says the convicted mass killer recently wrote a letter to ISIS leaders. In it, Hasan asked to become a citizen of the Islamic Caliphate. Hasan is on the Military's death row at Fort Leavenworth, Kansas. A Military court sentenced him to die for a November 2009 rampage at Fort Hood, Texas. He targeted unarmed soldiers who were preparing to deploy to Afghanistan, or just returning. 32 people were also injured in the attack. During his trial, Hasan claimed he objected to American Military involvement against Muslims in Iraq and Afghanistan.