Farooque Ahmed, a naturalized US citizen born in Pakistan, first drew the attention of law enforcement officials when he tried to obtain unspecified materials. He later became the target of an undercover sting, officials said.

The indictment says federal agents posing as extremists began meeting with Ahmed in April. At the meetings, held in Northern Virginia hotels, he allegedly agreed to conduct video surveillance of the stations.

At subsequent meetings, Ahmed provided a computer memory stick and a USB drive including images of Metrorail stations in the DC area. In September, he provided diagrams he had drawn of three stations and provided suggestions as to where explosives should be placed on trains to kill the most people in a simultaneous attack planned for 2011, prosecutors said.

He is also accused of later turning over video and sketches he made of the stations.

Officials stressed the public was never in danger, but the plot’s revelation has resulted in them asking riders and employees to be alert to suspicious activity. Metro Transit Police continue patrols while an anti-terrorism task force conducts random security sweeps and bomb-sniffing dogs and biological, chemical and radiological detection equipment are also used.

As details emerge about the FBI’s arrest of Ahmed, it’s clear the case shares some aspects with that of Hosam Smadi.

Smadi, 20, was caught in a sting last year in which a group of undercover FBI operatives convinced him they were Al-Qaeda sleeper cell members. The spent months building a rapport, and eventually Smadi chose a target — a downtown Dallas skyscraper — and took steps to blow it up. He was arrested after the bomb he was using turned out to be a fake.

Ahmed also was fooled into thinking that he was conspiring with Osama bin Laden associates, who were really undercover agents. It doesn’t appear that Ahmed got to the advance stage that Smadi did, actually triggering a fake explosive.

Agents learned of Smadi by his postings on extremist websites.

Another case similar to Ahmed’s is that of Michael Finton. He was arrested the same day as Smadi, Sept. 24, 2009, in Illinois after he drove a vehicle loaded with what he thought were explosives to the federal building in Springfield. The bomb, supplied by the FBI, was inert. He goes on trial in the spring.

Neighbors next to Ahmed say he was kindly to his next-door neighbors in the year he lived near them in suburban Virginia, but he was reserved to others, according to interviews.

Ahmed, 34, and his wife, Sahar Mirza-Ahmed, have a young son.

Jay Britton, who lives across the street from Ahmed, said that he was not particularly friendly. “Definitely not social,” he said.

Britton said he had run into Ahmed only a few times over the past year, and at most the two would exchange nods.

“He seemed like a loner,” added Shaya Fitzgerald, a next-door neighbor, told reporters.

Muslim leaders in Northern Virginia said that, as of late Wednesday, no one had reported knowing or having interacted with Ahmed at local mosques

His arrest has touched off a conversation about whether Ahmed might have initiated a plot or whether law enforcement officials had floated the idea to him, as has been suggested in other FBI sting operations.

“It’s a conversation that’s definitely going on in the community,” said Imam Johari Abdul-Malik, spokesman for Dar Al-Hijrah mosque in Falls Church. “At the same time, though, if you’re dumb enough and sick enough to want to work for Al-Qaeda, then you should be put in jail. If what the authorities accuse him of turns out to be true, I have very little sympathy for someone who plans something like that.”

Ahmed, who holds a bachelor’s in computer science from City University of New York, worked in Northern Virginia for Ericsson, a telecommunications company, and was pursuing a graduate degree online in risk management and data security at Aspen University.

If convicted, Ahmed faces up to 50 years in jail. The arrest will renew fears in the US that the biggest threat to national security comes not from groups operating outside the US but from homegrown terrorists.