NBC 5 Investigates has uncovered staffing records at Dallas/Fort Worth International Airport that detail concerns about a shortage of uniformed officers to protect the most public areas of the airport.

A recent internal police staffing plan said the D/FW police department's, "Current uniformed physical presence is insufficient based on threats and growth."

Airport records also show police response times at the airport have slowed in recent years and even a recent five year plan to boost the number of staff would still leave D/FW with fewer uniformed officers patrolling terminal and curbside areas than some other major U.S. airports.

D/FW is one of the busiest airports in the world, serving more than 60 million passengers a year.

In February, an NBC 5 investigation found police at D/FW Airport did not respond to cars left empty in front of the terminals. NBC 5 cameras recorded some cars sitting empty for 15 minutes or more with no visible response from airport police officers.

At the time, airport spokesman David Magana insisted there was no shortage of officers to deal with cars left at the curb.

"From the standpoint of having enough people, I don't think there's any question that we do," said Magana.

But after that interview, NBC 5 Investigates filed an open records request asking for records detailing police staffing at the airport.

The airport turned over documents including two police staffing plans. The most recent of which describes the number of uniformed officers as "insufficient" - particularly when it comes to the number of uniformed officers on what's known as the "non-sterile" side of the airport. That area includes the public ticket counter lobbies and curbside areas of the sprawling five airport terminals.

It's unclear who wrote the staffing strategy documents or who they were presented to, but they show in recent years the airport had just 12 uniformed officers assigned to patrol the five terminals on a typical shift. That's only two or three officers per terminal. Terminal D alone is more than 2 million square feet.

Records show five more uniformed officers were assigned to patrol in cars covering the rest of the 26-square-mile property, that is the size of the island of Manhattan. The property includes four hotels, cargo facilities, office buildings, a rental car center, restaurants, a golf course, two gas stations and a highway that runs through the middle of the airport.

When asked if those staffing levels seemed sufficient to cover an airport the size of D/FW, security expert Jeff Price responded, "I don't think so. For a large commercial service airport like D/FW is, they need more police officers."

Price is the author of a leading industry textbook on airport security and trains security officials across the country. After reviewing the D/FW staffing documents obtained by NBC 5 Investigates, Price said it appears that, "the airport police are saying we don't have enough staff and we need more people."

Price said a strong visible police presence is one of the best ways to deter attacks like the one that left more than 30 people dead in Brussels. In that attack terrorists targeted what's called the "non-sterile" side of the Brussels airport, around ticket counters outside of the security checkpoints that are softer targets.

"They're going to look for a place where they don't see police around and that's where they're going to do the activity," said Price.

Records show since 2014 D/FW Airport staff have been asking for more police.

The latest staffing strategy document requested 30 additional police officers over the next five years and 39 more security guards, or "security officers" as the airport calls them.

Financial records show the airport has approved at least six of those new police positions and 18 security officer jobs, but it is not clear if those jobs have been filled.

Airport staff has declined to answer questions and D/FW Airport CEO Sean Donohue sent a letter saying, "Given that D/FW Airport has long held a position of not publicly discussing security matters in detail, we will not consent to an interview."

Even if the airport got all of the 30 additional police officers and 39 security guards requested in that last staffing plan, the airport's records show the number of uniformed officers in the most public areas of the airport would still be less than at some other major airports.

An airport document titled "Industry Benchmarks" shows the D/FW Airport plan would ultimately put 32 police officers and security guards terminal and curbside on each shift.

But, the document said in Miami 75 officers patrol terminal and curbside each shift. At Los Angeles International Airport 115 security personnel patrol terminal and curbside and Atlanta's Hartsfield-Jackson International has 55 people assigned to those areas on each shift.

"We call it hardening the target, I want you to move elsewhere," said former L.A. police commander, LaPonda Fitchpatrick, who was in charge of staffing at LAX.

She said there's no replacement for uniformed officers when it comes to deterring terrorists and responding rapidly to threats.

"You know airports have multiple layers of security from electronics to other things that we can't even discuss here, but there is nothing like having that uniformed physical presence," said Fitchpatrick.

Records show adding 30 police officers at D/FW Airport would cost about $3 million over five years. But experts argue a lack of security can be even more expensive.

"It's very difficult to even calculate the amount of loss that occurs after an attack," said Fitchpatrick.

In his letter to NBC 5 Investigates, Donohue said the following about D/FW Airport and the security team:

It is considered to be among the best in the field and is widely acknowledged as a leader in its security and intelligence collaboration efforts with public safety partners regionally, nationally and globally.

D/FW Airport increased its budget in the past year alone to boost the number of airport public safety officers by over 10 percent.

Security at any airport involved much more than what is visible to the untrained observer, and is comprised of multiple layers of security, surveillance and robust intelligence sharing, all of which combine to protect D/FW Airport and those we serve.

All together there are approximately 2,500 people working to protect the public of the overall security matrix at D/FW.

It's unclear what's included in that 2,500 number. The airport's staffing records show about 175 police officers on staff and payroll records provided by the airport list about 100 security guards.

Police reports obtained by NBC 5 Investigates show police response times at D/FW Airport have declined in recent years.

In 2006, police responded to calls in five minutes and 37 seconds on average.

Last year that number climbed to six minutes and 52 seconds – one minute and 15 seconds slower than in 2006.

The number of calls for police has also increased dramatically. Calls were up 29 percent in 2014, the most recent call volume records provided.

In that February interview, Magana hinted that police leaders at the airport may want more help.

"You ask any police chief in America if they want more officers they will tell you and they will be able to use them" said Magana.

The day after that report aired in February, NBC 5 Investigates went back to the airport and saw officers out checking empty vehicles and tracking down drivers. But on more recent visits, NBC 5 staff has not seen officers patrolling the curbs in front of the terminals.

Now the airport's own records raise questions about whether there are enough uniformed police to protect the millions of people who pass through the airport each year. And, whether airport management is moving fast enough to address that concern.