This exclusive ABC News investigation found that American counterterrorism officials were investigating more than a dozen cases of possible terrorists who have slipped into the U.S. under the refugee program. With rare access inside current and ongoing major terrorism investigations, the in-depth investigative reports broadcast on "Nightline," "World News with Diane Sawyer" and "Good Morning America" told the story of how a little noticed arrest of two men in Kentucky led to a major national security investigation that commanded the attention of top officials, including President Obama. The Iraqis were not refugees fleeing persecution, as they had claimed to immigration authorities, but were al Qaeda-iraq terrorists who had targeted U.S. troops in northern Iraq with bombs and sniper attacks. A key piece of evidence was that the fingerprints of one defendant were located on an improvised explosive device stored in a box for six years in an FBI warehouse, which had been found buried in a Baiji, Iraq road by American soldiers in September 2005. Worse, the two Iraqi insurgents, who had lied their way into the U.S. as alleged refugees -- and escaped drawing scrutiny until they were serttled in Kentucky -- were plotting to ship- heavy arms back to Iraq in an FBI sting, and were also discussing U.S. Homeland revenge bombings, the FBI learned. ABC News was able not only to tell the story of this incredible counterterrorism investigation by the FBI with help from the U.S. military, but also connect a specific bombing in Baiji that killed four Pennsylvania National Guardsmen to the Iraqi defendants. The exclusive ABC News investigation, which was broadcast on the network's three major newscasts as well as online with stories and web extra videos, also broke the news of current FBI counterterrorism investigations of suspects inside the U.S. whose fingerprints are being checked with those lifted from devices in evidence at the FBI's secret "bomb library," where ABC News was shown 100,000 IEDs collected from warzones in Iraq, Afghanistan, Pakistan, Yemen, Somalia and elsewhere.