NOGALES, Ariz. (AP) -- Border Patrol agents had a clue some tunnel-digging might be going on when a young man answered a knock on the door of a home just north of the Mexican border holding a pickaxe.

Agents had noticed an unusual amount of noise late Wednesday afternoon coming from inside an abandoned home across the street from the border fence in the downtown area, spokesman Rob Daniels said. The house was just west of the U.S. Customs and Border Protection parking lot.

Agents first encountered a man standing outside the home, whom they talked to and took into custody; then they knocked on the door after continuing to hear noise from inside, Daniels said.

"It's like the fox coming to the door of a henhouse with a chicken in its mouth," he said of the second man who opened the door with the tool in hand.

Agents took a third man into custody after discovering an unfinished tunnel about 2 1/2 feet in diameter and going down about 20 feet, where it dead-ended.

The tunnel was incomplete, but "all that separates it from the border is the road," Daniels said. "It could go right underground to Mexico."

The three men, 18-, 19- and 20-year-old Mexican nationals, remained in custody but had not been charged yet, Daniels said.

Over the past decade, authorities have discovered numerous drug tunnels, including several that were completed and used to transport narcotics, near downtown Nogales.

"Most tend to be connected in one way or other with drainage tunnels," Daniels said. "This one was not."

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