Here's a cool story about information collected by the FBI over the last few years:

There was the suspected militant fleeing Somalia who had been arrested on a drug charge in New Jersey. And the man stopped at a checkpoint in Tikrit who claimed to be a dirt farmer but had 11 felony charges in the United States, including assault with a deadly weapon.

The records suggest that potential enemies abroad know a great deal about the United States because many of them have lived here, officials said. The matches also reflect the power of sharing data across agencies and even countries, data that links an identity to a distinguishing human characteristic such as a fingerprint.

"I found the number stunning," said Frances Fragos Townsend, a security consultant and former assistant to the president for homeland security. "It suggested to me that this was going to give us far greater insight into the relationships between individuals fighting against U.S. forces in the theater and potential U.S. cells or support networks here in the United States."
WAPO, 3 pages, damn good read.