A Pakistani-born suburban father was trying to enlist in a terrorist organization in January and was eager to become a martyr when he unknowingly walked into an FBI sting and began helping plan a purported attack on the Washington subway system, according to court documents.

What followed was an elaborate ruse in which Farooque Ahmed was given intelligence-gathering duties and coded information in a Quran by two individuals posing as al-Qaida operatives as part of the supposed plot to kill commuters on the nation’s second-busiest subway system.

Ahmed, 34, of Ashburn, Va., was caught on FBI surveillance video discussing his firearm, martial arts and knife skills and offering to teach those deadly tactics to others, according to an FBI affidavit unsealed Thursday.

The affidavit by FBI agent Charles A. Dayoub describes meetings beginning in mid-April between Ahmed and the pair he believed were al-Qaida operatives and the actions Ahmed took to advance the fake plot. The operatives were really working on behalf of the U.S. government, according to a federal law enforcement official who requested anonymity to discuss details of the case.

Ahmed was arrested Wednesday, just weeks before, the FBI says, he planned to make the annual religious pilgrimage to the Islamic holy city of Mecca in Saudi Arabia. The case represents the latest in a recent string of would-be terrorist attacks that officials say were aided, hatched or carried out by U.S. citizens.

Dayoub said Ahmed had an associate who also tried to join a terrorist group and accompanied Ahmed while he conducted surveillance of subway systems. There was no immediate information about the associate’s identity, whether the bureau might be looking for the associate or whether the individual was cooperating with authorities. Justice Department spokesman Dean Boyd would provide no details on the associate’s identity.

The FBI and White House have said the public was never in danger because FBI agents had Ahmed under tight surveillance before the sting was begun and until his arrest.

Ahmed’s lawyer, federal public defender Kenneth Troccoli, declined to comment on the case Thursday.

A naturalized U.S. citizen, Ahmed was a contractor with the telecommunications company Ericsson Services Inc. Company spokeswoman Kathy Egan said he never worked on the company’s government contracts, including ones with the Pentagon. Ahmed never had access to classified information, Egan said.

Dayoub’s affidavit disclosed that the FBI learned in January that Ahmed and an associate were trying to make contact with terrorist groups to help participate in jihad against U.S. forces overseas.

Dayoub wrote that Ahmed was lured by an e-mail to the first meeting detailed, on April 18, in the lobby of a hotel near Washington Dulles International Airport. As the FBI secretly videotaped the encounter, Ahmed accepted a Quran that contained “documents providing code words for locations to be used for future meeting,” the affidavit said.

Ahmed told a purported al-Qaida operative he had come to the meeting because “he wanted to fight and kill Americans in Afghanistan,” Dayoub wrote.

Dayoub also said the FBI had learned that Ahmed bought, or tried to buy, weapons in May 2008 and February 2009. Authorities believed he used firearms to train for his goal of traveling to Afghanistan to kill Americans.

The agents who searched Ahmed’s town house Wednesday were looking for computers, associated equipment, software and instruction manuals for the equipment, according to the warrant application which was unsealed with Dayoub’s affidavit. They also applied to seize Ahmed’s 2005 Honda Accord and all assets in his bank account.

Ahmed has been indicted on charges of attempting to provide material support to a designated foreign terrorist organization, collecting information to assist in planning a terrorist attack on a transit facility, and attempting to provide material support to terrorists.

According to the indictment:

—Ahmed took video of four northern Virginia subway stations — Arlington Cemetery, Courthouse, Pentagon City and Crystal City, which is near the Pentagon — and monitored security at a hotel in Washington. In a series of meetings at hotels in northern Virginia, Ahmed provided the videos to someone he believed was part of a terrorist organization and said he wanted to donate $10,000 to help the overseas fight and collect donations in a way “that would not raise red flags.”

—In a Sept. 28 meeting in a Herndon, Va., hotel, Ahmed suggested that terror operatives use rolling suitcases instead of backpacks to blow up the subway. During that same meeting, Ahmed said he wanted to kill as many military personnel as possible and suggested an additional attack on a Crystal City subway station.

Ahmed is merely the latest alleged example of homegrown terrorism and FBI stings directed at the problem.

Last week, a Hawaii man was arrested and accused of making false statements to the FBI about his plans to attend terrorist training in Pakistan. In July, a Virginia man was caught trying to leave the country to go fight with an al-Qaida-affiliated group in Somalia. And in May, Faisal Shazhad, a naturalized citizen from Pakistan, tried to set off a car bomb at a bustling street corner in New York City.

The FBI has made several cases with agents working undercover: Last year, authorities arrested a Jordanian national after he tried to detonate what he thought was a bomb outside a Dallas skyscraper. In an unrelated case, authorities in Springfield, Ill., arrested a man after he tried to set off what he thought were explosives in a van outside a federal courthouse. In both cases, decoy devices were provided to the men by FBI agents posing as al-Qaida operatives.

A LinkedIn page that was created for Farooque Ahmed identifies him as a network planning engineer with a bachelor’s degree in computer science from the City College of New York in 2003, during the same period that other records showed he had been living in New York.

Neighbor Margaret Petney said Ahmed moved in his Ashburn, Va., town house about a year and a half ago with his wife and young child, and that they wore traditional Muslim clothing.

Ahmed’s wife, Sahar, joined the Hip Muslim Moms, a support group for women with children under 5 years old, and brought her young son to play dates with other mothers, said group organizer Esraa Bani. She had moved to the area and was looking for a mothers’ group when she joined. She was very quiet and kept to herself.

Petney observed that “they didn’t seem to be too friendly with anybody.”