EXCLUSIVE: How the FBI Foiled a 2012 Plot to Bomb the US Capitol

— -- The arrest Wednesday of an Ohio man who allegedly plotted an all-out assault on the U.S. Capitol was not the first time the FBI nabbed someone for such a plot through an undercover operation – and surveillance video, exclusively obtained by ABC News from that earlier case, shows just how far homegrown radicals are willing to go.

“Let’s do it man, I don’t want to keep thinking about it too much,” 29-year-old Amine El-Khalifi said inside a hotel room in February 2012, just days before he planned to launch his attack with a suicide vest strapped to his chest and a MAC-10 automatic gun in one hand. “Let’s do it.”

That commitment to his cause came just minutes after Khalifi tried to familiarize himself with the submachine gun that a man he thought was an associate of al Qaeda had just handed him. In fact, the supposed al Qaeda operative was an undercover FBI agent.

“It’s a striking moment,” the current head of the FBI’s Washington Field Office, Assistant Director In Charge Andrew McCabe, told ABC News’ Pierre Thomas in an exclusive interview. "Theme that you have to take away from seeing a tape like this is the understanding that these folks are out there.”

McCabe said “recent developments around the world,” such as the deadly assault on a satirical magazine in Paris two weeks, further highlight the evolving threat from terrorists.

“It’s a significant problem,” he said. "There is a population of young folks, largely young men, who connect with that extremist message. They are inspired by it.”

Before becoming enchanted with the radical messages of al Qaeda leaders posted online, Khalifi enjoyed “going to bars, drinking alcohol, using cocaine and ecstasy, and spending money on flashy clothing and accessories,” according to court filings in his case.

Weeks before he was to carry out his attack, Khalifi went with undercover FBI agents to a quarry in West Virginia, where they were to test a bomb they had supposedly built.

After the bomb goes off, Khalifi can be heard on surveillance video saying: “Brother, this is not strong enough.”

In his interview with ABC News, McCabe said the FBI currently has dozens of such undercover investigations underway.

“We don’t even consider the use of these sorts of undercover strategies until we are convinced that the [suspect] clearly intends to do what they said they intend to do,” McCabe said, adding that suspects are always “many, many opportunities to back away from their plans.”

“And time and time again, the subjects we’re most concerned about say very clearly they intend to go forward,” according to McCabe.

McCabe rebuffed any suggestion that the FBI “entrapped” Khalifi, a Moroccan citizen who was in the United States illegally.

“Just watch that tape,” McCabe said. “I think it’s clear from the way he expresses himself what he’s committed to do and the actions that he took to get there.”

Even Khalifi’s attorney acknowledged in court filings that his client wasn’t entrapped.

“However, he ... was enabled by the FBI, who, as part of its ‘sting,’ helped Mr. El-Khalifi with the means, method and motivation for the attack,” federal public defender Ken Troccoli wrote in a memo to the federal judge overseeing the case. “This included monetary incentives (paying his debts and promising ‘martyrdom payments’ to his parents), the provision of weapons and explosives with training on how to use them, logistical advice, and religious reinforcement by a cadre of (supposed) like-minded Islamists.”

In June 2012, Khalifi pleaded guilty to one count of trying to use of a weapon of mass destruction, admitting that over more than a year he hatched a plan to attack U.S. government sites, ultimately deciding to strike the U.S. Capitol.

In the surveillance video obtained by ABC News, Khalifi can be seen buying nails from a Home Depot outside Washington.

“I got thick ones, not thin ones. The one [that is] going to make damage,” he says in video from later that day.

In the video he also says of U.S. senators: “I want those people.”

ABC News was able to obtain only a small portion of the hours of surveillance video created during the investigation into Khalifi. ABC News filed a Freedom of Information Act request with the FBI for all of the surveillance video, but that request was denied. An appeal is pending.

Troccoli, Khalifi’s defense attorney, declined to comment beyond what he said in court filings in 2012. In those filings, he said Khalifi “bears no ill-will against the American people.”

In fact, Trocolli wrote, Khalifi “is relieved that his attempted crime was foiled and that no one was actually injured.”

Khalifi is currently serving a 30-year sentence.

On Wednesday, the FBI arrested Christopher Lee Cornell, 20, of Green Township, Ohio, for allegedly plotting an ISIS-inspired attack on the U.S. Capitol, where he hoped to set off a series of bombs aimed at lawmakers, whom he allegedly considered enemies. He has been charged with attempting to kill a U.S. government official.

The FBI first noticed Cornell several months ago after an informant notified the agency that Cornell was allegedly voicing support for violent “jihad” on Twitter accounts. The informant then helped the FBI build a case against Cornell.