NEW YORK — U.S. Customs officials and Arizona police have seized copper ingots worth more than $1.5 million allegedly stolen from producer Asarco LLC in what law enforcement officials say could be an inside job at the company’s copper smelter in Hayden, Ariz.

Acting on a tip, Arizona police stopped a flat-bed truck from the Hayden facility on a state highway in September and recovered 49 copper ingots, according to the state Department of Public Safety. Police traced the copper back to a residence in Marana, Ariz., where 56 more ingots were recovered.

Over the next month, Customs officials in California recovered 359 copper ingots at the ports of Los Angeles and Long Beach in six containers that were labeled as scrap metal, the department said.

"They were taking them from the mine to a drop house," Carrick Cook of the Arizona Department of Public Safety told AMM. "The drop house would rearrange it and cover it up. They were burning it and making it look like scrap metal."

The ingots were on their way to China when they were discovered, with three containers already having left the seaport on two ocean cargo carriers, according to investigators. The other three containers were stopped one day before they were scheduled to depart for Hong Kong.

"With so many ingots stolen, we are under the strong impression that one or more people inside the mine are involved," Cook said. "There were several different transportation methods with multiple people involved in this."

Cook said that considering the complexity of the alleged theft, a larger crime network might be discovered as the investigation continues. "This might be a nationwide program (in which) they’re stealing metal alloys from all over the country and shipping them to China," he said.

Tucson, Ariz.-based Asarco, a subsidiary of Grupo Mexico SAB de CV, is offering a reward of up to $50,000 for information leading to the arrest and conviction of anyone involved in the alleged theft.

A company spokesman was not available for comment.