Waad Ramadan Alwan, 30, arrested on terrorism charges May 31 along with Mohanad Shareef Hammadi, 23, was not on the list because the FBI did not put his fingerprint information into databases used to flag potential security risks, Homeland Security national protection Undersecretary Rand Beers said.
Sen. Joe Lieberman, Ind-Conn., whose Homeland Security and Governmental Affairs Committee called Beers to testify, said he intended to call the FBI to ask about its handling of Iraqi suspects' security information.
The FBI had no immediate comment.
Alwan and Hammadi, living legally as refugees in Bowling Green, Ky., are accused in a 23-count indictment of conspiring to send weapons and money to al-Qaida in Iraq. Alwan was also charged with attacking U.S. soldiers in Iraq.
The two have pleaded not guilty and face life in prison if convicted.
Sen. Rand Paul, R-Ky., criticized the federal program that allowed nearly 60,000 Iraqis, including Alwan and Hammadi, become refugees.
"I don't fault you for missing the needle in the haystack," Paul was quoted by The (Louisville, Ky.) Courier-Journal as saying to Beers. "You've got to make the haystack smaller. You know? You need to admit less people. There's no reason we should be admitting 60,000 people."
Janice Jacobs, assistant secretary of state for consular affairs, defended the Iraqi-admission policies, telling the panel granting special-immigrant visas for Iraqis working on behalf of the U.S. government was intended to fulfill a "special responsibility" to these people.
Security screening under the Iraqi resettlement visa program has intensified in the past six months, and especially since the May arrests of Alwan and Hammadi, to ensure that no refugees "pose a threat to the security of the United States," Jacobs said.
Beers said all Iraqi refugees in the last three years are being re-screened, Beers said.