A man linked to the cross-border tunnel that was found Friday in Calexico has pleaded not guilty to possessing about 1,000 pounds of marijuana found in a truck he was driving.

Jesus Bernardo Aguila Agundez made his plea at the El Centro federal courthouse Monday, according to U.S. authorities.

Aguila's arrest Friday paved the way for U.S. investigators to obtain a search warrant that same day to enter a Calexico house from which the truck had reportedly been seen leaving.

Inside, they found a 400-foot-long cross-border tunnel with lighting, ventilation and a water pump system. Mexican authorities, notified of the tunnel, found its opening in a house on the Mexicali side of the border.

Drug Enforcement Administration special agent Dan Simmons wouldn't say how a multiagency task force had grown suspicious about the Calexico house.

U.S. authorities were conducting surveillance for several weeks on cars leaving the house on East Second Street, according to court records.

On Friday, they watched a blue truck back halfway into the house's garage and someone load unidentified items onto it, according to the records.

They followed the truck to a swap meet and afterward.

Calexico police then stopped the truck and found 100 packages of marijuana covered by a tarp, according to the records.

No arrests were reported on the Mexican side, but officials there did find marijuana residue on their side of the tunnel, according to a news release from the Mexican Attorney General's Office.

The Arellano Felix drug cartel has been linked to drug tunnels in the past, but Mexican and U.S. authorities wouldn't say whether this tunnel was used by a particular group.

The Mexicali region's drug network is believed to be mostly controlled by suspected drug traffickers Ismael Zambada and Joaquin Guzman, who are rivals of the Arellanos.

The tunnel's interior dimensions were 3½ feet by 4 feet, and it had been built about 20 feet underground, according to agency spokesman Simmons. There was about 8 inches of standing water in the tunnel, and a pump was found on the Mexican side, he said.

Such pumps are often found in tunnels where underground water tends to seep into the spaces.

The tunnel had been reinforced with wooden beams and planks. U.S. authorities also found four skateboards that may have been used to scoot the drugs through the tunnel, which had a concrete floor.

“I don't see a bunch of kids practicing with their skateboards down there,” Simmons said.

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