Two months before allegedly killing five and wounding eight in the Fort Lauderdale airport, Esteban Santiago walked into an FBI office in Anchorage, Alaska with a loaded handgun magazine appearing "agitated" and reporting "terroristic thoughts," officials told reporters. He insisted that the CIA was forcing him to watch ISIS videos, the officials added.

The FBI passed him to local authorities, who took him to a mental health facility. The police took custody of his handgun, which was in his vehicle.

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Four days later, he was freed. The police gave him his gun back.

Santiago now joins a list of people — including Orlando nightclub shooter Omar Mateen, alleged Manhattan bomber Ahmad Rahami and Boston marathon bombing planner Tamerlan Tsarnaev — whose troublesome behavior brought them to the attention of the FBI before they committed violent acts.

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That fact pattern has renewed calls from experts who believe the FBI needs to extend some greater level of scrutiny to people who appear threatening but whose actions do not merit a traditional criminal investigation.

FBI officials are strongly pushing back, arguing that Santiago’s interactions in Anchorage are the kind that happen in FBI offices across the country nearly every day, and that the bureau has neither the resources nor the legal mandate to track such people.

John Cohen, a Rutgers University professor and former counter terrorism coordinator at the Department of Homeland Security, has long argued that the FBI should borrow a page from the Secret Service, which regularly monitors and assesses people, including mentally disturbed people, who have voiced threats against the president and other protectees but whose actions have not reached the level of a crime. Agents will visit them in their homes, track their social media and otherwise seek to intervene with them, Cohen said.

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If a person is deemed a risk but not a criminal, the Secret Service employs any number of strategies to prevent an attack, Cohen said, including facilitating mental health treatment.

Cohen argues that the Attorney General’s guidelines governing FBI criminal procedures, which require a finding of a crime or a threat to national security to move forward with a field investigation, should be expanded. A system should be put in place, he says, to refer potential threats to state and local authorities and mental health counseling, without losing track of them.

"We take more of a behavioral and psychological approach, [the] FBI tends to take a legal approach."

"Guidelines governing the evaluation of potential terrorist threats need to be adjusted so that the FBI has greater flexibility when assessing the risk posed by someone who has been brought to their attention," said Cohen, who is studying mass casualty attacks. "Behavioral assessment protocols and threat management strategies have proven highly effective in preventing assassinations school shootings and other acts of violence, and those same tools should be available on a consistent basis to counter terrorism investigators."

As of now, "if it doesn’t cross the legal threshold, it’s a hand-off approach," said Seamus Hughes, a former U.S. intelligence analyst who is deputy director of the Program on Extremism at George Washington University.

"There is not a standard process when it comes to mental health or a 15-year-old kid who speaks in favor of ISIS. There is no non law enforcement approach to that."

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A senior FBI counter terrorism official, who was not authorized to be quoted by name, said it wasn’t practically feasible for the FBI to investigate people who did what Santiago did in Anchorage, nor is he sure a majority of the public would stand for it.

"The American public through Congress has long said it doesn’t want the FBI conducting investigations without cause — spying on citizens," he said.

The public and the news media focus on the handful of people who went on to violence after interactions with the FBI, he lamented. What that misses, he said, is that the bureau receives as many as 50,000 terrorist tips a year, and conducts more than 15,000 assessments. In contrast, the Secret Service is dealing with fewer than 10,000 threats yearly, according to former senior Secret Service official Jim Helminski.

And nearly every day, he added, a mentally disturbed person comes into an FBI office expressing disjointed, troubling thoughts. There is no way federal law enforcement could or should investigate or track every such person, he said.

"In hindsight, absolutely the gun should have been kept away from this guy," he said, "but how do you make that into a predictive model without going overboard and violating people’s rights?"

The FBI already conducts too many terrorism investigations, said Michael German, a former FBI agent who is now a civil liberties expert with the Brennan Center for Justice’s Liberty and National Security Program at the NYU School of Law. Most of those probes lead nowhere, he said, dulling the bureau’s senses to actual threats.

"The problem that we see over and over again is that the knee-jerk reaction to horrible events Is to give law enforcement and intelligence more authority to investigate more people," he said. "This is a fatally flawed strategy."

Former senior Secret Service official Helminski told NBC News he is not sure what more any law enforcement agency could have done in the Santiago case.

However, he said, the FBI could probably benefit from adopting some of the Secret Service’s approach to persons of interest. The Secret Service often works up behavioral profiles of people who make threats to protectees, asking them to sign waivers to obtain their medical records, getting in touch with relatives, logging their names into a database and sometimes visiting them years later.

"We take more of a behavioral and psychological approach, while the FBI tends to take a legal approach," he said.