A Sierra Leonean former National Guard soldier has been charged with plotting to help the Islamic State of Iraq and Syria (ISIS) and contemplating a Fort Hood-style attack against the U.S. military.

MB Jalloh

Mohamed Bailor Jalloh, a naturalized U.S. citizen from Sierra Leone, was arrested on July 3 after purchasing a “Stag Arms assault rifle” from a gun dealer in Virginia, the U.S. Attorney’s for the Eastern District of Virginiasays in a press release.

He is expected to make an initial appearance Tuesday in federal court in Alexandria.

Court records made public Tuesday indicate Jalloh is a former member of the Army National Guard who says he quit after hearing lectures from radical cleric Anwar al-Awlaki.

A court affidavit spells out a three-month sting operation in which Jalloh said he was thinking about carrying out an attack similar to the 2009 shootings at Fort Hood, which left 13 people dead. Court records indicate the FBI saw Jalloh purchase an assault rifle Saturday.

Jalloh’s sister, Fatmatu Jalloh, said she hadn’t seen the charge against her brother but denied he would be helping ISIS.

Jalloh was charged with attempting to provide material support and resources to ISIS, a designated federal terrorist organization, prosecutors say. He faces up to 20 years in prison if found guilty.