According to the US Justice Department Aws Mohammed Younis al-Jayab travlled overseas after he had been admitted as refugee to the US so vetting would not have found anything.

“According to the allegations in the complaint, the defendant traveled to Syria to take up arms with terrorist organizations and concealed that conduct from immigration authorities,” said U.S. Attorney Wagner.  “While he represented a potential safety threat, there is no indication that he planned any acts of terrorism in this country. I commend the FBI’s Joint Terrorism Task Force for their dedicated work on this matter.”