According to the court affidavit, Harroun told the FBI that he estimated shooting 10 people during fighting in Syria but didn't know if any of them were killed.
His attorney questioned the FBI agent who wrote the document and asked if the agency could verify he shot people and said there is no video of him actually firing an RPG.
FBI agent Paul Higginbotham said the government had no independent confirmation.
Kamens said after Harroun was taken to the al-Nusra camp he wanted to return to his own group. He said Harroun had told authorities he was afraid if he didn't participate in attacks with al-Nusra its members would assume he was an American spy and kill him.
Harroun served in the U.S. Army from 2000 to 2003 but was never stationed overseas.