"It is your constitutional right to spout anti-American beliefs," said agent Steven Hersem, who helped supervise the Khalifi investigation. "We spend a lot of our time trying to figure out if someone is an actual threat or not."
In Khalifi's case, the conversation before the quarry explosion convinced them.
"That was an epiphany for me that this man is a definite threat and he must be stopped at all costs," said Bryan Paarmann, assistant special agent in charge of counterterrorism at the FBI's Washington Field Office.
Initially, Khalifi was no different from many young men who find their way to the United States. He had been born in Morocco and visited Florida with his father at age 16. He overstayed his visa and eventually moved to Northern Virginia, where he worked odd jobs as a cook, busboy and salesman.
He got into mixing and producing music. For a time, agents said, he was a fixture on the D.C. club scene, where he started to use cocaine, marijuana and ecstasy.
In 2007, Khalifi was arrested and charged with assault after an argument at a club. At some point after the arrest, agents said, he decided to be a more devout Muslim and was drawn to the teachings of radical clerics on the Internet.
An FBI analyst noticed in July 2010 that Khalifi had responded to a Facebook posting by a known terrorist in Afghanistan seeking help for his cause. Six months later, a confidential informant told agents that Khalifi was hanging out with friends — some of whom were on the FBI's radar — in an apartment in Arlington County, Va., when someone pulled out an AK-47 and two revolvers. Khalifi agreed with his friends that the war on terrorism was a war on Muslims and that they should be ready for battle, according to the informant.