School shooting highlights tough gap between warning about and eliminating a threat

Attorney General Jeff Sessions, remarking on the tragedy the following day, said, "We can and must do better."

"It is just too often the case that the perpetrators have given signals in advance," Sessions said Thursday. "We've had advance indications, and perhaps we haven't been effective enough in intervening immediately to deal with that. I suspect it appears that we've seen that again in this case."

But law enforcement faces serious challenges in preventing frequent, high-profile gun violence, even with some alerts from the public and warning signs lurking on social media.

One of the foremost challenges: Threats pour into the FBI constantly.

"I don't even know how to quantify it," said former FBI special agent Josh Campbell, a CNN law enforcement analyst.

The difficulty of sussing out usable information from myriad threats is further compounded by the reliability of the warnings, the strength of existing law enforcement information, the public's ability to discern what is cause for concern and instances where law enforcement powers butt up against civil rights.

Connecting the dots

A law enforcement official said the FBI allegedly received at least two threat reports about the suspected Florida shooter, and in both cases, the agency did not share information with local law enforcement. One of the threat reports came in the form of a screenshot of a YouTube user with the suspect's name who said, "Im going to be a professional shooter."

Campbell said the office that received a threat could search the FBI's database, and that the agency's ability to follow up from there would hinge on "what level of credibility and specificity" it can determine.

The FBI special agent in charge of the Miami division, Robert Lasky, said Thursday that the bureau had received a tip about the YouTube comment last year, but that FBI database reviews and checks were "unable to further identify the person."

CNN legal analyst Carrie Cordero said the FBI's inability to link the comment to the eventual suspected shooter was reason enough to ask questions about what might have gone wrong.

"No one wants to criticize law enforcement when they're in the moment of responding to a major event like this," Cordero told CNN's Brooke Baldwin. "But there are legitimate questions about what they knew about the individual and whether they took all of the steps that were available to them."

Unless the FBI can identify the person, Campbell said, its options for moving past that point were nil.

"An FBI investigation is only as good as the information that comes into the FBI," Campbell said.

Asked if, given all these challenges, the FBI ever prevents a shooting like the one in Florida, Campbell said successes are difficult to assess and that in many ways it would be trying to prove a negative.

"It's hard to quantify something you interdict, something you stop," he said.

The government's investigative powers also can come into conflict with civil liberties and due process concerns. Law enforcement needs to demonstrate probable cause to obtain a warrant, mental health professionals and the mentally ill have privacy rights, and the Second Amendment has led to limits on how the government regulates firearms.

Mental health and firearms

Over the entire issue of repeated, deadly, high-profile incidents of gun violence is the political debate on what, if anything, new legislation could accomplish to deter attacks.

Democrats and other gun control advocates have called again for some kind of gun legislation in response to the shooting, raising universal background checks and restrictions on military-grade firearms.

A source told CNN's Evan Perez that the suspect used an AR-15 style firearm he had bought within the past year after passing a background check.

Meanwhile, President Donald Trump asserted on Twitter that there had been obvious warning signs about the shooter and "neighbors and classmates knew he was a big problem."

An attorney for the suspected shooter's host family said the family "didn't see a mentally ill person," while Broward County Sheriff Scott Israel said the alleged gunman's social media posts were "very disturbing."

Across the country, people may be reluctant to go to the authorities with their concerns, due to a distrust in law enforcement, a lack of confidence in them or fear that doing so will have an adverse affect.

"People sometimes don't want to go to law enforcement," Campbell said. "They think, well, this might ruin this person's life."