The investigation into a shootout between different groups of Federal Police in Mexico City’s international airport last month has not resulted in the arrests of the suspected killers, but it offers further indication of the airport’s importance for criminal groups.

The airport in Mexico’s capital city earned a wave of new headlines on June 25, when two Federal Police officers are believed to have shot three of their colleagues to death. The two alleged shooters are Daniel Cruz Garcia and Zeferino Morales Franco, who disappeared following the incident and remain at large. A third agent who was reportedly acting as an accomplice, shift leader Bogard Lugo de León, also fled following the shooting.

According to a Federal Police spokesman, the pair of alleged shooters were participants in a smuggling ring that was bringing cocaine into Mexico on a flight from Peru that arrived the morning of June 25. When they were confronted by the three agents who had been investigating the ring for a year and a half, Morales Franco (who was carrying the drugs which had just arrived in the country) and Cruz Garcia opened fire.

The incident comes ahead of a period of significant transition for the Department of Public Security (or SSP, for its initials in Spanish), the cabinet agency which houses the Federal Police. Genaro Garcia Luna, the controversial secretary who has emerged as one of the figures with the greatest amount of influence on security policy in the Calderon administration, will almost certainly be leaving the post in December, as President-elect Enrique Peña Nieto brings in his own team upon taking over. Peña Nieto has promised to increase the role of the Federal Police in order to reduce the role of the armed forces, although it remains to be seen if the SSP emerges as a locus of security policy the same way it was under Calderon.

While the group of officers was linked to a smuggling group run by a figure known only as El Chino, subsequent reports from the government indicated that the Sinaloa Cartel currently controls the Mexico City airport. The organization, often described as Mexico’s most powerful criminal network, is headed by Joaquin “El Chapo” Guzman and Ismael “El Mayo” Zambada, with men loyal to Zambada controlling the cocaine shipments that arrive at the airport.

Over the years, the Sinaloa Cartel has exercised intermittent control over the air traffic passing through Mexico City. For most of the past decade, the Beltran Leyva Organization, or BLO, dominated the airport, which essentially gave Guzman and his group unfettered use of the facility.

However, the 2008 split between Beltran Leyva brothers and the Sinaloa bosses eliminated this easy access, and threw control of one of the nation’s most important transport hubs into flux. After the 2009 death of Arturo Beltran Leyva in a shootout with Mexican marines, control of the airport devolved to his erstwhile subordinate, Edgar Valdez Villarreal. Valdez was subsequently arrested in August 2010, which cleared the way for Zambada and his partners to take over.

The amount of passenger and cargo traffic passing through the airport, which lies in the geographical center of the country and serves as a hub for both international and domestic flights, helps explain its appeal to criminal groups. With almost 28 million passengers and 409,000 tons of cargo arriving per year, Mexico’s busiest airport offers a wealth of legitimate traffic which helps mask the illicit shipments of cocaine and methamphetamine precursor chemicals.

While Mexico City has long been the prize possession, criminal groups have also sought access to other airports. For years, the BLO also maintained control of the Cancun airport, which is second only to Mexico City’s in terms of passenger traffic, and lies just a short flight across the Caribbean from Colombia and Venezuela.

Even before the most recent shootout, evidence of drug traffickers exploiting airport facilities and their employees frequently emerged in recent years. Three employees of Aeroméxico were arrested in Madrid in 2010, after smuggling 135 kilos of cocaine out of a flight leaving from Mexico City, and months later, pilot from the same airline was arrested in Madrid with roughly 40 kilos of cocaine.

And while its relevance to the actual movement of drug shipments is indirect, one of the most infamous crimes in recent Mexican history took place at the Guadalajara airport, another of Mexico’s biggest: a hit team searching for Guzman, sent by the Arellano Felix brothers in 1993,  confused their target’s vehicle with the limousine of Cardinal Juan Jesús Posadas Ocampo, and riddled it with bullets. Guzman escaped the attempt on his life, but Posadas Ocampo and six others were murdered.