PORTLAND, Maine (AP) — The high electricity consumption of a home, its cardboard-covered windows and odor of marijuana drew law enforcement’s attention to an illicit grow operation off the beaten path in rural Maine.

The bust of the home with a hidden grow operation and seizure of nearly 40 pounds (18 kilograms) of processed marijuana marked the latest example of what authorities describe as a yearslong trend of foreign nationals to exploit U.S. state laws that have legalized cannabis for recreational or medical use to produce marijuana for the illicit markets in the U.S.

The U.S. Drug Enforcement Administration is investigating international criminal organizations that are operating illegal marijuana grows in about 20 states, including Maine, Attorney Garland Merrick Garland told the Senate Appropriations Committee this week, in response to a question raised by Republican Sen. Susan Collins of Maine.

Federal law enforcement officials said there currently are about 100 illicit grow operations in Maine, like the one in Passadumkeag, about 60 miles (96.5 kilometers) north of Bangor, and about 40 search warrants have been issued since June.

In Passadumkeag, Xisen Guo, a naturalized U.S. citizen born in China, has been accused of transforming the house into a high-tech, illicit grow operation, according to court documents unsealed this week.

He was ordered held without bail Friday on federal drug charges, making him the first person to be charged federally in such a case in Maine. A detention hearing is scheduled for Monday.

The Internal Revenue Service and Department of Homeland Security, along with the FBI and DEA and local law enforcement, are working together to get to the bottom of the illicit grow operations in Maine, Garland said.

The state legalized adult consumption of marijuana, but growers must be licensed by the state. The Maine Office of Cannabis Policy said Guo was operating an unlicensed operation, according to court documents.

The illicit grow operations across the U.S. began cropping up several years ago. In 2018, U.S. authorities arrested a Seattle woman, conducted raids and seized thousands of marijuana plants during an investigation of an operation with Chinese ties. Oklahoma officials learned straw owners in China and Mexico were running illegal operations after marijuana was legalized by the state for medical purposes in 2018.

The legality of marijuana consumption and cultivation in those states tends to provide cover for illegal grow operations, which may draw less attention, officials said. The marijuana is then trafficked in states where it’s illegal.

In Maine, U.S. Attorney Darcie McElwee said thwarting illegal growing operations with international connections is a priority for law enforcement, “and we will continue to marshal every tool at our disposal in this effort as appropriate.”

Law enforcement officials know the tell-tale signs.

Police zeroed in on the Passadumkeag operation in part because of the home’s utility bills reviewed by deputies. After the home was purchased for $125,000 cash, the electricity use went from about $300 a month to as high as nearly $9,000, according to court documents.

That’s consistent with heat pumps, costly lighting and other gear needed to grow marijuana, investigators said. The home owner, a limited liability company, upgraded the electric capability to double what is found in a typical Maine home, according to documents.

Guo’s attorney didn’t immediately return a call from The Associated Press. Two others who were at the home at the time of the police raid in February were released and not charged.

McElwee said law enforcement — from local and county police to the FBI and DEA — are starting to make headway with “dozens of operations” shuttered over the last several months.

“The possible involvement of foreign nationals using Maine properties to profit from unlicensed marijuana operations and interstate distributions makes it clear that there is a need for a strong and sustained federal, state and local effort to shut down these operations,” she said.

Law enforcement officials also continue to investigate who is directing the operations and where the profits are going, she said.