border patrol agent sergio martinez. martinez: the first tunnel was discovered in 1990 in douglas, arizona. and since then, they have encountered 183 tunnels within the tucson sector and the southern border. and most recently in nogales, arizona, they have actually team in nogales where their daily duties are to go find tunnels. sharyl: border patrol agents use remote controlled robots to investigate the tunnels. the majority of them, at least 100, have turned up in the town of nogales, arizona. some just steps from the border crossing teeming with federal agents. 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 ou