A US man who wrote he was “ready for jihad” before buying a one-way ticket overseas to try joining the Islamic State group was sentenced to prison on Tuesday after he sobbed to the judge: “I am an American.”

Leon Nathan Davis III of Georgia state was sentenced to 15 years, the maximum punishment allowed. Davis, 38, pleaded guilty in May to seeking to help a known terrorist organization.

He was arrested at the Atlanta airport last October trying to board a flight to Turkey. Davis later said his plan was to be smuggled into Syria so he could join the Islamic State group as a recruiter and an English teacher.

During his sentencing on Tuesday, Davis told the judge he had been “brainwashed” by writings and online propaganda of radical Muslims not long after he converted to Islam while imprisoned for cocaine trafficking a decade ago.

Despite his apologies and acknowledgement of wrongdoing, prosecutors insisted Davis was far from harmless.

Assistant US attorney Carlton Bourne showed the judge a photograph Davis posted online of himself holding a shotgun and surrounded by other weapons. Bourne said Davis added the caption: “Ready for jihad.”

About a year before buying his plane ticket, Bourne said, Davis posted online: “One of my greatest desires is to kill Zionists and bring down Israel and the United States of America.”

Despite being a convicted felon, Davis owned six rifles, four handguns and two shotguns, according to prosecutors who originally charged him with illegal gun possession. That charge was dropped as part of a plea deal.

Authorities in the US have charged several dozen people in the last year with trying to fight alongside the Islamic State and other militants or with lending them material support.