Federal authorities have discovered a sophisticated drug-smuggling tunnel that went from a home in Mexico to an abandoned fast-food restaurant in Arizona.

The Homeland Security Investigations division of the Department of Homeland Security says it got word in April that there was a tunnel leading to an old Kentucky Fried Chicken restaurant that’s not in operation in San Luis, Arizona, just about 200 yards (180 meters) north of the border.

Police began trailing the owner of the abandoned building, Ivan Lopez, and arrested him this month after finding several packages of methamphetamine, cocaine, heroin and fentanyl in the back of his truck.

That arrest led to a search at his home and the old restaurant, where agents found a hidden tunnel that led to a house in Mexico and was large enough for people to freely walk through.

“One of the things that tunneling does tell us is that as we increase infrastructure, resources, patrol, that’s forcing them to go to more costly routes into the U.S.,” Scott Brown, the special agent in charge for HSI, told the Associated Press on Thursday.

Brown said his agency has been seeing an increase in tunnels, which are expensive to build and take long periods of time. He said a functioning tunnel can cost cartels hundreds of thousands of dollars to build.

“Tunnels are a time-consuming venture, but it has definitely increased since the border security measures have ramped up,” Brown said.

Authorities don’t know how long the tunnel had been used, but Lopez only bought the property in April.

According to court documents, the government believes Lopez is a well-trusted cartel member. He was seen taken packages out of the building several times before his arrest on Aug. 13, the court papers said.

Lopez is being held in federal detention without bond because he is considered a flight risk, according to court documents.

His attorney, Paul A. Ramos, did not respond to a request for comment.

The use of tunnels for drug trafficking has been a major issue for decades and has been brought up by opponents of the proposed border wall, who say tunnels will help smugglers circumvent it.

In 2016, authorities busted a nearly half-mile tunnel running between Otay Mesa, California, and Tijuana, Mexico. HSI has a tunnel task force and the Customs and Border Protection agency has a tunnel detection and technology program, all to tackle the nearly 200 cross-border tunnels that have been discovered since 1990.

(AP)