this tunnel on the border town of naco is one of the longest, at more than 900 feet anone of the most recent discoveries. here in southe just a few hundred yards from the mexican border. that's it, the fence over there. and you can see right here in what looks like a shed next to a house, that's where the drug tunnel is. martinez: so apparently they were coming in through the shed, parking, opening the door, loading up the vehicle, and then pulling the stuff out of the tunnel. sharyl: and tell us how it was discovered? martinez: it was discovered by human intelligence. they pulled a vehicle over, and the guy had over 4,000 pounds of contraband in his vehicle, and up, and they came to the house with a warrant and arrested them all the individuals in the , house. and we come in here. here is the actual tunnel. so they had a lift gate. they were bringing the narcotraffics and all the stuff they had, all the narcotics. they were bringing it above, they had a lift since they were so heavy. they were just bringing it up, straight up. sharyl: how long was an operation like this going on for