The tip and the Facebook posting got the bureau's attention. Agents combed public records and reached out to a network of informants to learn more about Khalifi. The informants told agents that Khalifi wasn't just expressing support for terrorist groups and jihad; he wanted to participate in what he considered a holy war.
Within a month or so, FBI agents decided that Khalifi was dangerous enough to warrant an intensive inquiry. They tapped his phones, monitored his Internet use and tracked his movements with teams of surveillance agents. The work confirmed what their sources had been saying, and FBI officials said it was time to get a better sense of what Khalifi had in mind by sending in undercover agents.
By late summer of last year, agents determined that Khalifi was brokering car sales on the Internet and was looking to buy a Toyota Prius. One of the FBI's undercover agents, a man who called himself "Hussien," posted in an online advertisement that he was selling such a car.
The agent soon heard from Khalifi, and they met in an office building parking lot on a cloudy and warm Thursday in September 2011. They chatted about the car and then hit it off, the FBI said, speaking in Arabic about their pasts as Muslims from Arab countries.
Khalifi also spouted violent rhetoric about Jews, Israel and U.S. policy. Hussien played it loose, agents said, mostly nodding in agreement.
"That was a good first meeting," said the case's lead agent, who spoke on the condition of anonymity for security purposes. "It set up a follow-up meeting. We were establishing a relationship."
The men met again the next day, and Khalifi bought the car. Soon, Hussien and Khalifi were hanging out and chatting on the phone about religion and automobiles. The agents lined up another deal, this time for a beat-up Volkswagen, to further develop the relationship.