Now, to the shocking discovery in california. Federal authorities uncovering a massive and sophisticated drug tunnel near san diego running underground to tijuana. Millions of dollars in drugs seized. Three suspects now in custody. Abc's pierre thomas in washington has more on that for us. Good morning, pierre. Reporter: Good morning, robin. It's an epic game of cat and mouse between the u.S. Government and the mexican cartels. We're about to show folks at something that will give them the scale and scope of drug running from the mexican border. It was designed to move illegal narcotics by the ton. It has electricity, a ventilation system, so smugglers can breathe underground, and rail system to transport drugs. Built by engineers and architects. They're sophisticated. They're high-tech. Reporter: The tunnel begins in a tijuana, mexico, warehouse, snaking its way under the border to this building, in an australia complex outside san diego. It is four feet high and three feet wide. Spanning more than one-third of a mile long. Six football fields in length. The supertunnels are capable of moving massive amounts of drugs. In this case, authorities seized more than eight tons of marijuana and hundreds of pounds of cocaine destined for the u.S., Valued at more than $12 million. They intended to move a large amount of narcotics into the tunnel, and before they could get one pound into this country, they were stopped. Reporter: This is the eighth tunnel found in the san diego area since 2006. A similar tunnel was found only blocks from the new one. Over 75 tunnels have been discovered since 2008. When you see these tunnels, you truly understand that the multimillion-dollar corporations in mexico are huge. And you get a sense that americans smoke a hell of a lot of weed. Robin? All right, pierre, on both