"We get fingerprints off of rocket that we can tie biometrically to an individual in Iran"

"...But how is the U.S. so sure that the weapons and training are coming from Iran?
“We have a very comprehensive understanding of where the rockets are manufactured,” Maj. Gen. Jeffrey S. Buchanan, chief spokesman for the U.S. military in Iraq, said in an interview. “We can identify what factory they were made in by certain markings. We’ve seen markings recently of rockets that were manufactured in Iran in 2010. These are not things that were just buried in old cache sites. They continue to come across the border in very large numbers.”
U.S. officials say three Shiite militia groups — the Promised Day Brigade, Asaib Ahl al-Haq and Kataib Hezbollah — are responsible for the deaths of at least 18 U.S. troops in the past seven weeks. The groups have been trained and supplied by Iranian Revolutionary Guard special forces, who U.S. officials say are crossing the border into Iraq to provide training and materiel.
Singling out the Kataib Hezbollah, Buchanan said: “We get fingerprints off of a certain cache or a certain rocket that we can tie biometrically to an individual who lives in Iran, he’s a top leader of Kataib Hezbollah, he lives in Iran, he is trained by the Quds Force. All of that together is a very compelling set of evidence.” ..."