Teams of undercover police officers fan out across Los Angeles International Airport targeting what they call the "insider threat."
This potentially serious hazard isn't coming from travelers, but from those who work at the airport itself.
Law enforcement officials say airports around the country routinely monitor the thousands of employees, who must undergo a criminal background check and get fingerprinted. At LAX, the nation's second busiest airport, police screen employees and check IDs as part of a multi-agency operation.
CNBC was allowed exclusive access to a recent insider threat police operation as well as inside security operations at the airport, videotaping areas never before seen by the public.
"I think about everything. I think about the possibilities," said Los Angeles Airport Police Chief David Maggard Jr. "And then, what we try to do is get that information from the other people that have maybe had an experience with the tragic event or with the threat. And we try and gather that information and apply it here."
Maggard oversees the largest aviation police force in the U.S. with about 1,100 police and other staff. The airport's "zero tolerance" policy for employees means any employee can be randomly searched at any time.
During the insider threat operation in July, an airport ramp worker was arrested for an outstanding DUI warrant.
"The key to our program is they don't know when they're going to be checked. We can check people as they come in. They'll check people as they go. We'll check people when they're here working. And so we do have a comprehensive program," he said.
Maggard gave CNBC a tour of the Airport Response Coordination Center, known as the ARCC, where employees monitor more than 3,500 cameras throughout LAX around the clock. Threats, small and large at airports around the country, are also watched, as well as social media feeds.
"Our analysts are helping connect the rest of the region," Maggard said. "So we want to make sure that if we hear of something that would be concerning to an airport 100 miles from where we are, we want to make sure we're communicating that."
LAX was the first airport to hire two full-time intelligence analysts in 2014, the year after a shooter killed a TSA officer and wounded three people there.
"We've learned that anything can happen here," Maggard said. "And we want to make sure that we spent a lot of time learning from that incident, as we have studied other events around the world that have threatened airports. As a result, we've increased our technology. We've added cameras. We've added officers in the terminal area. Our profile is larger."
As LAX undergoes a massive expansion, it plans to eventually double the number of cameras, many of which are hidden, throughout the complex.
Outside, police randomly screen vehicles entering LAX as part of a program called Operation Safe Entry. In addition, cars are periodically screened with hand-held radiation detection devices, which is considered another counterterrorism measure.
"If you want to turn around and leave the airport, they have the ability to do that," Maggard said. "But if they want to come into the airport, there are some legal limited abilities for us to do some searches. We're looking for anything that may be harmful to the airport environment."
The airport spends more than $200 million annually on security, according to LAX officials. One federal government study found that federal and local spending at airports nationwide totals at least $8 billion, a figure the study considered a low estimate.
Most airport security operations are hidden. For example, CNBC videotaped an LAX police officer checking sharp knives in an airport restaurant kitchen. All of those knives are subject to inspection and must be properly inventoried.
"We have to make sure is that we account for all the knives that's in what's called the sterile area, that's past the TSA screening checkpoint," Police Officer Sean Foley said. "Most of the problems we come into is accountability, meaning they're not checking out the knives properly. Thankfully, we haven't run across too many knives missing. What has happened we have knives missing, but they go into the trash. We have video cameras inside a lot of the restaurants and we do have video of them going into the trash."
The two intelligence analysts assigned to LAX acknowledge one of their main concerns is the insider threat.
"If somebody is trying to smuggle bulk cash or drugs, they're getting paid to put something on an aircraft. And the concern is, when are they going to know that it's a bomb and not drugs that they're being asked to put on board?" senior intelligence analyst Michelle Sosa told CNBC.
Anthony McGinty, who is also a senior intelligence analyst, said the TSA has been "very good at securing above the wing. But often times, below the wing and what goes on around the airplane in many versions, that's what we're worried about. If you can put drugs in a bag, that's another step to put a bomb in the bag. So it's a serious threat."
"I think a lot of people even forget these days why we have this level of security," Sosa said. "People don't remember any more that even what they see today is because of 9/11. Terrorists have been going after aviation even before 9/11. So even it hadn't happened that time, they were going to do something. And they were going to continue to do something related to aviation. And I imagine that we'd be somewhere similar to today."
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