Robertson, also known as "Abu Taubah," had been incarcerated since 2011 on charges of tax fraud and illegal gun possession. After his arrest and subsequent conviction on those charges, prosecutors sought to add a terrorism enhancement to his sentence, a sentencing guideline modification that would have sent the Islamic scholar to prison for up to 20 years.

Instead, following the judge's rejection of the enhancement, he was sentenced to time served and ordered released immediately.

Robertson's case attracted national attention after prosecutors attempted to argue earlier this year that the contents of his book collection constituted evidence of his connection to terrorism. Prosecutors singled out roughly 20 titles from the more than 10,000 e-books Robertson owned, highlighted a selection of controversial passages, and used that to argue that he should be sentenced as though he were a terrorist.