A former U.S. soldier has been charged with trying to join the Somali Islamist militant group al Shabab.

The U.S. Department of Justice said in a statement Monday Craig Baxam secretly converted to Islam shortly before leaving the army in July of last year. The statement says the 24-year-old flew to Kenya and paid for transportation to Somalia, where they say he intended to join al Shabab and “live under (Islamic) Sharia law.”

He was arrested by Kenyan police near Mombasa, before crossing the border.

Baxam, who trained in cryptology and intelligence in the U.S. army and served in Iraq and Korea, could face up to 15 years in prison if found guilty.

Al-Shabab is trying to overthrow the United Nations-backed government and set up a strict Islamic state.