An Iraqi-American who fought in the Syrian civil war was arrested in Texas on Thursday–not for any crimes related to his past militancy, but for actions related to his posting online of what federal agents described as “an oath to Abu Bakr al-Baghdadi, the leader of ISIL.”

The feds are alleging that Bilal Abood lied to investigators when he told them that he had never swore fealty to the head of the Islamic State.

While Abood acknowledged to agents that he knew it was a crime to lie to the FBI, he denied that the messages he posted on Twitter amounted to a pledge of allegiance. In the June 2014 postings cited by the Justice Department criminal complaint released Friday, however, Abood allegedly wrote that he “pledge[s] obedience to the Caliphate Abu Bakr al-Baghdadi. Here we renew our pledge to the Caliphate Abu Bakr al-Baghdadi come on supporter where is the pledger.”

The FBI additionally claimed that a search of Abood’s computers also revealed that he “had been on the internet viewing ISIS atrocities such as beheadings, and using his twitter account to tweet and retweet information on al-Baghdadi.”

Abood’s case offers a glimpse into how the Justice Department is monitoring and making life difficult for those alleged to be extremist Islamic State sympathizers. The complaint notes that the “FBI is investigating numerous individuals who have traveled or are attempting to travel to Syria in order to involve themselves in the fighting that has consumed Syria for more than three years.”

In an interview with agents in September 2013, after he returned to the United States from Syria, Abood said that he was there fighting for the Free Syrian Army—a collective of US-supported rebels battling to topple Syrian President Bashar al-Assad. He said that he had stayed in an FSA camp, but told investigators that the FSA and the al-Qaeda linked al-Nusra Front “actively collaborated in achieving objectives, exchanging equipment, and committing attacks.” Eventually, Abood “became frustrated with a lack of action,” according to the complaint, and returned to the United States. He isn’t being charged for taking part in Syria’s brutal civil war.

Abood had been under the FBI’s watch since 2013, when he initially attempted to leave the United States for Iraq from Dallas Forth Worth International Airport. He told agents, who eventually prevented him from boarding the flight, that he was visiting family. He went to Mexico a month later, and from there traveled to Syria via Turkey.

According to the New York Times, Abood had worked as an interpreter in Iraq for the US military before immigrating to the US. In 2009, he was granted citizenship. The paper also noted that Abood last year told an ABC news affiliate in Dallas that the FBI was hounding him because he refused to cooperate with them.