The United States is struggling to confront the stubborn persistence of homegrown terrorists, even as it has repeatedly proven able to disrupt broader, organized plots from overseas.
A week after the deadly massacre in Orlando, Fla., there are few signs of a major intelligence failure, even though gunman Omar Mateen had been interviewed three times in the last three years.
But the episode illustrates the near-impossibility of detecting “lone wolves” before their diet of online propaganda and internal hatred turns into violence.
“It is an exceptionally challenging issue for the intelligence community, security and law enforcement to deal with,” CIA Director John Brennan told the Senate Intelligence Committee this week.
Killers like Mateen can be inspired by extremists on the internet and make their plans “without triggering any of those traditional signatures that we might see as a foreign terrorist organization tries to deploy operatives here,” he added.
The obstacles have only increased as the Islamic State in Iraq and Syria (ISIS) has evolved from a centralized Middle East extremist group to a digital multimedia behemoth, eager to claim anyone acting in its name.
On Monday, the Senate this will take up four separate gun control proposals, including measures to prevent suspected terrorists from buying arms, though all appear doomed due to deep partisan divides.
But officials say there are precious few legal avenues to prevent the next massacre, especially as ISIS’s external propaganda machine keeps spinning.
“Access to weapons makes sense for our leaders to focus on, because they don’t understand the motivations,” said Robert Pape, the founding director of the Chicago Project on Security and Terrorism. “If you don’t have a clue as to what’s really motivating, because this is new, then you have no choice but to focus on access to weapons.
“And it makes perfect sense.”
The image of Mateen remains clouded.
Officials said that he watched online videos from ISIS and similar extremists, which helped inspire him to gun down 49 people at a gay nightclub last weekend, in the deadliest mass shooting in modern American history.
He also pledged allegiance to ISIS in the hours before he was killed by police, fulfilling a key requirement for the group to grant recognition.
However, he appeared to have no direct communication with ISIS leaders in their self-proclaimed caliphate in Syria. And while the group was quick to embrace him, other motivations also appear to have been at play, including a history of domestic violence and struggles with his own sexuality.
“Ideology played a role, but it was not a major role,” said Matthew Levitt, a former FBI analyst and director of the Washington Institute for Near East Peace’s counterterrorism and intelligence program. “What appears to have been important to him is the empowering message of strong, militant Muslim groups.”
That makes Mateen and those like him particularly hard to catch.
“I anticipate we’re going to have many more cases like Mateen’s where ideology is not the main issue,” Levitt said. “We’ll have many where ideology is the main issue.
“But the thing to keep in mind here is there’s no profile.”
Without records of communication, travel or financing from someone else, it’s difficult for the government to have detected that Mateen had larger plans.
During the FBI’s investigation into him in 2013 and 2014, officials placed Mateen under surveillance, introduced him to confidential informants and interviewed him twice. But at some point they had to drop the case, since there was no evidence to keep going.
Months later, he was interviewed as part of another FBI investigation, but apparently did not raise enough of a red flag to prompt a new federal probe.
In the meantime, he was able to go on watching videos and accessing websites that encouraged him to act out.
“What ISIS has done is created a middle ground idea here between inspired [attacks] and command-directed [attacks],” said Pape. “What ISIS has is a set of inter-related materials that help produce their attacks much the way a movie producer produces a movie.”
That technical knowledge helps their adherents carry out the deadliest attacks possible.
“Because they’re the executive producer, they’re able to get highly lethal results that used to take command-direction to get.”
The way security officials respond to ISIS's growing connection with supporters around the world is also continuing to evolve.
Before the Senate Intelligence Committee this week, Brennan said that his agency is looking at both the “upstream” creators of the content and the “downstream propagation.”
But intelligence agencies' abilities are limited. The CIA does not have ultimate control of the internet, Brennan noted, and can run into both legal and technical problems when it tries to have content taken down.
In cases like Mateen’s, where the government appears to have no reason to continue pursuing an investigation, responsibilities might fall to social workers or local communities to step in, analysts said.
Some Senate lawmakers have pushed for more funding at the FBI to keep up with the roughly 1,000 cases of homegrown extremism it is investigating. But FBI Director James Comey has said that he has all the resources he needs.
There are ways to try and reduce the threat of homegrown radicals, said Lorenzo Vidino, the director of George Washington University’s program on extremism, but none to eliminate it.
“Nothing is perfect. Nothing is bulletproof,” Vidino told The Hill.
“There’s no silver bullet here.”