Inside the drug tunnels

LESTER HOLT, anchor: Now to a remarkable discovery and a record pot bust along the nation's border with Mexico . Federal agents have found a massive secret passage, an elaborate tunnel equipped with a rail system and an elevator used to smuggle drugs into the US. Tonight NBC 's Mark Potter takes us inside.

MARK POTTER reporting: Federal agents say it's the most elaborate smuggling tunnel they've seen in years, more than 600 yards long with wooden walls and floors.

Unidentified Man #1: The tunnel has lighting, and it does have good air flow, indicating that there's some type of ventilation system forcing air in from Mexico .

POTTER: The tunnel begins on the Mexican side of the border in a warehouse at the Tijuana airport . To lower drugs into the tunnel , there is a hydraulic elevator which leads to a rail system where an electric cart waits to carry marijuana to the US side. On steps leading upward, the tunnel emerges inside another warehouse in Otay Mesa , California .

Unidentified Man #2: Looks like the tunnel goes down about 30 feet here.

POTTER: This enhanced aerial photograph shows the tunnel going beneath a runway, roads, a big parking lot, and the border fence .

Mr. DEREK BENNER (United States Immigration and Customs Enforcement): All considered, a highly efficient mechanism to move narcotics in an underground environment.

POTTER: Police say they seized 32 tons of marijuana, a record for a single tunnel . Much of it was hidden in pumpkin boxes. Federal agents suspect it's the work of Mexico 's powerful Sinaloa drug cartel , currently harvesting its ever-increasing fall marijuana crop. Authorities say especially this time of year, traffickers need tunnels to smuggle huge drug loads to the US.

Ms. LAURA DUFFY (United States Attorney): If they can't cross the border above ground, they attempt to tunnel underneath it.

POTTER: The Sinaloa cartel is headed by Joaquin Guzman , known as " El Chapo " or "Shorty." Since his daring escape from prison 10 years ago, Mexican authorities have been unable to touch him.

Mr. GEORGE GRAYSON (College of William and Mary): He has the police under his thumb. He controls much of the judicial system in his state and neighboring states, and he's virtually an untouchable.

POTTER: In the last four years, American agents have found more than 75 illegal tunnels crossing from Mexico to the US, but say this one is the most sophisticated. Mark Potter , NBC News, Miami.