Atlanta (CNN) The breakup of a gun smuggling ring allegedly involving a current and former Delta Air Lines employee has exposed what a New York prosecutor described as an "egregious breach of security" at Hartsfield-Jackson Atlanta International Airport.

Brooklyn District Attorney Kenneth Thompson said Tuesday that the investigation was "deeply troubling" -- not only for the havoc the gun running unleashed on the streets but because of the vulnerability to acts of terrorism on air travel that it revealed.

"If they can put guns on the plane this time," he told reporters, "they could have easily put a bomb on one of those planes."

Two men worked together to smuggle guns and ammunition on at least 20 flights from Atlanta to New York from May to December, officials said.

"We have an egregious breach of security" at Hartsfield-Jackson Atlanta International Airport because airport employees "are not required to go through screening," said Thompson.

In total, 153 guns were recovered as part of a complex investigation that Thompson outlined by using charts and surveillance video during a press conference in New York.

Eugene Harvey, who worked for Delta at the Atlanta airport, was arrested at his home in Atlanta on Monday, authorities said.

JUST WATCHED Official: Suspect sold over 100 guns Replay More Videos ... MUST WATCH Official: Suspect sold over 100 guns 04:29

According to Harvey's arrest warrant affidavit, here's how the operation worked:

-- Harvey used his security clearance to help provide guns to a passenger named Mark Quentin Henry after Henry cleared security.

-- Henry, the former employee, allegedly brought the firearms in his carry-on luggage on at least five flights from Atlanta to New York between May 1 and December 10.

-- During that time frame, Henry supplied 129 handguns and two assault rifles to co-conspirators in New York, the affidavit states.

-- One of those co-conspirators ended up selling the firearms to an undercover New York police officer.

"Gun violence is tearing our country apart," Thompson said. "In Brooklyn, far too many people have been victims of gun violence."

Reese McCranie, spokesperson for the Atlanta airport, said officials have cooperated with the FBI, the Transportation Security Administration and other agencies and was reviewing its security.

"As part of the TSA- and airport-approved multi-layered security plan, all employees must pass extensive criminal history record checks, security threat assessments, and security training prior to being approved for access to secured areas," he said in a statement. "Additionally, employees are subjected to continuous vetting and random inspections."

In a statement, the TSA said it took "the potential for insider threats at airports very seriously."

"TSA administers security threat assessments and airport criminal checks for all airline employees prior to receiving credentials and access privileges," the statement said. "This is a recurring vetting process that involves random checks. TSA continues to closely partner with law enforcement on this investigation and, where possible, will use the findings from the investigation to improve current processes."

Thompson praised Delta for being cooperative from start to finish of the undercover probe.

Henry was arrested in New York on December 10 after landing at John F. Kennedy International Airport with 18 handguns in his bag -- seven of which were loaded, the affidavit says.

"The problem at this airport in Atlanta is that the employees don't have to go through screening," Thompson said. "Henry knew that. Henry would give Harvey the guns outside the airport. Harvey would go through. All he had to to was badge himself in ... and he's in the terminal with the guns."

Henry told investigators that he had flown from Atlanta to New York with the 18 firearms and associated ammunition in his carry-on bag, FBI task force agent George Taylor wrote in the affidavit.

So how could a man get more than a dozen guns on a flight in his carry-on backpack?

"Had the eighteen firearms been inside the Oakley bag when Henry passed through TSA screening, the firearms would have been discovered," Taylor wrote.

"Accordingly, I reasonably believe the eighteen firearms bypassed security."

The 'backdoor method'

Mary Schiavo, a CNN aviation analyst, said the suspects apparently "took advantage of known loopholes" in airport security. Baggage handlers and other airport employees don't have to go through a concourse screening as passengers do, creating a "backdoor method" for airport employees to smuggle materials, she said.

"That's literally been a loophole since 2002," when the TSA was established, she said. "There was a big issue on cost."

When she was inspector general of the Transportation Department for six years ending in 1996, Schiavo raised the "same kind of warning" about the screening of airport employees.

"This is an important wake-up call. I just hope Washington and the airports heed it," she said.

Schiavo said that "it will take a lot of expense and manpower to close that loophole."

At the news conference, Thompson held one of the weapons allegedly smuggled by Henry -- an AK-47.

"This gun can shoot through a car door," he said. "It can shoot through an apartment door. It can shoot through a bullet-proof vest. In November, Mr. Henry brought this gun on a Delta commercial airliner to New York."

Transfer in men's restroom?

On the morning of December 10, the affidavit says, baggage handler Harvey used his security clearance to enter Delta's employee parking lot and then the secure area of the airport.

"Employees entering this area are not subjected to screening by the Transportation Security Administration (TSA), neither at the time of entry into the employee parking lot, nor upon entry to the internal secure/restricted area at Hartsfield-Jackson," the affidavit states.

Surveillance video showed that on the same morning, the passenger Henry cleared security with a black Oakley backpack. He then went to sit down at the airport's Concourse B.

According to Taylor, that's when Henry started texting Harvey. Moments later, Harvey entered a men's restroom in Concourse B. And Henry followed.

After one minute, the affidavit says, Henry walked out of the restroom with the backpack.

The criminal complaint also says on several occasions this year, Harvey used his security clearance to enter the secure Delta employee parking lot -- even though he was supposed to be off or on sick leave.

And on each of those dates, Henry boarded a flight from Atlanta to New York.

Delta spokesman Morgan Durrant told CNN the airline is cooperating with authorities.

"We take seriously any activity that fails to uphold our strict commitment to the safety and security of our customers and employees," he said.

Thompson said Henry allegedly boarded 20 flights with guns between May and December.

"We were fortunate that we were able to get all the guns that they tried to put on the streets of Brooklyn," he said.