While an Iraqi refugee spent two years in the U.S. plotting to help al-Qaida attack American soldiers in Iraq, court documents say, federal authorities unknowingly had evidence that already linked him a roadside bomb in his home country in 2005.

National security experts said the 21-month lapse in linking fingerprints from the bomb to the suspect shows poor communication among the several federal agencies in charge of anti-terrorism efforts.

"That's very disturbing," said Charles Rose, a criminal and military law professor at Stetson Law School in Gulfport, Fla., who served as an Army intelligence officer and a judge advocate general. "That's a problem."

Even without the fingerprint match, the FBI had begun investigating 30-year-old Waad Ramadan Alwan a few months after he was allowed to come to the U.S. as a refugee. Still, experts say the crime-scene evidence from Iraq could have led to a faster arrest.

He and 23-year-old Mohanad Shareef Hammadi, both of Bowling Green, Ky., were charged last week with plotting to send explosives, guns and missiles to Iraqi insurgents after an investigation that began in September 2009. Neither is charged with plotting to launch attacks inside the United States, and authorities said their weapons and money didn't make it to Iraq.

But Alwan's fingerprints had been lifted off an improvised explosive device found near Bayji, Iraq, in September 2005.

Before he entered the U.S.as a refugee in April 2009, he had to provide a set of fingerprints for a security check. A statement from the Department of Homeland Security acknowledged that gaps prevented authorities from connecting the refugee fingerprints to the bomb until January 2011.

"Rarely do you get that much evidence," said Frank Cilluffo, director of a homeland security studies program at George Washington University who also served as White House domestic security adviser to President George W. Bush. "It's that much more troubling that it wasn't caught."

Alwan is charged with conspiracy to kill a United States national, conspiracy to use a weapon of mass destruction and attempting to provide material support to terrorists. Hammadi is charged with attempting to provide material support to terrorists and knowingly transferring, possessing or exporting a device designed or intended to launch or guide a rocket or missile.

The men pleaded not guilty to the charges Tuesday, and are in federal custody pending a detention hearing.

Alwan and Hammadi, also a refugee, entered the United States four months apart in 2009. The FBI and federal prosecutors wouldn't say how the two men were granted refugee status and wouldn't address why Alwan's fingerprints weren't matched sooner to those taken off the IED.

Iraqis seeking refugee status in the United States have two ways of getting it. One is to apply through the U.S. Refugee Admissions Program, and the other is via a special exemption that is made for those who assisted U.S. forces.

Applicants must show they have a fear of persecution due to their race, religion, nationality, membership in a social group or political opinion, according to the Department of Homeland Security. They must submit to an interview by an immigration officer and two security checks.

According to a report on the Department of Homeland Security website, even if authorities determine a person meets the definition of a refugee, that person "may nonetheless be inadmissible to the United States due to criminal, security or other grounds, and therefore ineligible for refugee resettlement."

The report, "Refugees and Asylees: 2010," shows that almost 19,000 Iraqi refugees were allowed into the United States in 2009, accounting for more than a quarter of all refugees admitted to the U.S. that year and the highest number of Iraqis on record. In 2010, the number totaled 18,016.

A Department of Homeland Security official, who requested anonymity because the investigation is ongoing, said Tuesday that the gaps that allowed Alwan and Hammadi to slip in have been filled.

The official said the agency now checks people repeatedly as new information becomes available.

The official said Homeland Security started comparing applicant information against a broader set of data after the arrest of Umar Farouk Abdulmutallab, who has been charged with trying to blow up a passenger jet over Detroit on Christmas 2009 by using a bomb in his underwear. Authorities have worked backward on prior applicants to run fingerprint matches.

Bob Carey, vice president of resettlement and migration policy for the International Rescue Committee in New York, said the newer, stricter screening methods are working.

"These people are not representative of the refugees who come to the United States from Iraq," said Casey, whose agency helps resettle Iraqi refugees.

Court documents say Alwan told an informant working for the FBI that he began insurgent activities in Iraq in 2003 and was captured by Iraqi authorities in May of 2006. It was unclear in court documents what, if any charges Alwan faced in Iraq or when he was released.

Federal prosecutors and the FBI declined to address Alwan's arrest in Iraq or give details of which refugee admissions process he used.

Alwan entered the United States on April 22, 2009, while Hammadi entered the country on July 20, 2009. State Department statistics show that 230 Iraqi refugees resettled in Bowling Green between October 2007 and June 11, 2010.

Court records don't explain how Alwan was granted refugee status. Criminal complaints against the men don't specify what led investigators to Alwan, and Hale and Fries wouldn't say. Alwan was already being watched when authorities say he recruited Hammadi early this year.

Cilluffo questioned how many people linked to terrorist groups could have entered the country before the 2009 Christmas bombing attempt because their fingerprints weren't checked or because they had no prints on file in any database.

But even fingerprinting isn't going to keep every would-be terrorist out of the country, because many haven't left any evidence behind to be found, Cilluffo said.

"It's not fool proof," Cilluffo said. "That's a concern."