From NBC:

Four men in the group were charged in two separate indictments for allegedly conspiring to sell 153 firearms that were mostly bought in Georgia and destined for the streets of Brooklyn, from May to December 2014, the King’s County District Attorney’s office said in a statement.

One of the men in the group was employed as a Delta bag handler who smuggled weapons — some loaded —into the Hartsfield-Jackson airport in Atlanta, where he handed them off to an accomplice, Mark Quentin Henry, who flew to New York, federal law enforcement officials said.

After the Patriot Act and TSA making everyone go through naked body scanners, guns still got on planes. This same technique could be used by terrorists to smuggle bombs on airplanes. The government was too concerned with passengers and not focused on security in general.