SAN DIEGO (AP) — A Mexican trucker was sentenced Monday to nearly 16 years in prison for his role in two major drug tunnels along the U.S.-Mexico border, marking the end of one of the most prominent cases since the secret passages began turning up about a decade ago.

Daniel Navarro, 45, apologized in a soft voice to his family and a federal judge for his role in tunnels that linked warehouses in San Diego and Tijuana and resulted in seizures of a combined 52 tons of marijuana. The long passages raided in November 2010 were lit, ventilated and equipped with rail cars.

"This defendant is a significant, significant player," said Sherri Hobson, an assistant U.S. attorney. "This defendant is right in the middle of it."

Navarro, who pleaded guilty in June to conspiracy to distribute marijuana, knew where the tunnels were and had keys to one warehouse, Hobson said. He was in frequent contact with one driver who was caught with nearly 10 tons of marijuana in his truck and told authorities that he previously worked with Navarro on large loads. Navarro led another driver on the freeway who was arrested with 14 tons of marijuana in his truck.

Holding the warehouse keys shows Navarro was a "trusted, trusted person" in the tunnel operations, said Hobson, who sought a 30-year prison sentence.

Defense attorney Victor Sherman acknowledged Navarro had a part in both tunnels but sought to play down his role. He asked for a 10-year sentence.

"There's no evidence that he's a manager or supervisor of anybody," he said.

U.S. District Judge Larry Burns sentenced the Mexicali native to 15 years and eight months in prison. He said Navarro was "up to his hips" in smuggling the huge marijuana loads, but the sentence was barely half the length that prosecutors wanted.

Navarro became a legal U.S. resident in 1999 and worked as a trucker in Southern California, his attorney said. He worked construction briefly in Tulsa, Okla., last year.

As U.S. authorities have tightened their noose on land over the last decade, tunnels have emerged as a major tack to smuggle marijuana.

More than 70 passageways have been found on the border since October 2008, surpassing the number of discoveries in the previous six years. Many are clustered around San Diego, California's Imperial Valley and Nogales, Ariz.

Copyright 2011 The Associated Press.