BANGOR, Maine — The Mexican man who oversaw what law enforcement officials have called the largest marijuana farm in Maine’s history pleaded guilty Tuesday in U.S. District Court to a drug conspiracy charge and one count of harboring illegal aliens.

Moises Soto, 53, of Nuevo Leon, Mexico, could be a key witness next year when the trial of others charged in the alleged drug conspiracy and marijuana distribution ring are scheduled to be tried.

Malcolm French, 50, of Enfield, Robert Berg, 49, of Dexter, Rodney Russell, 48, of South Thomaston, and Kendall Chase, 55, of Bradford were indicted along with Soto in September 2012 by a federal grand jury. All have pleaded not guilty and are free on bail.

Haynes Timberland Inc., a Maine corporation owned by French, also has denied charges stemming from the Sept. 22, 2009, seizure of 2,943 marijuana plants.

By pleading guilty, Soto, who speaks English and Spanish, admitted that he ran the farm using undocumented workers. He has been held without bail since his arrest March 15 at the McAllen, Texas, Port of Entry. He is not expected to be sentenced until after charges against his co-defendants have been resolved.

Soto was indicted in September 2012 by a federal grand jury on one count each of conspiracy to manufacture 1,000 or more marijuana plants and manufacturing 1,000 or more marijuana plants, two counts of maintaining a drug-involved place and three counts of harboring illegal aliens. All charges except for the two to which Soto pleaded guilty are expected to be dismissed when he is sentenced.

It took more than 60 state and federal law enforcement officers almost a week in the fall of 2009 to harvest the high-quality marijuana plants worth an estimated $9 million from a remote area in Township 37, near the town of Wesley and about 10 miles off Route 9, according to previously published reports.

The massive pot plantation was found after a tip was left on the Maine State Police Troop J website, according to the U.S. Attorney’s Office. When police flew a plane over the site, people on the ground set fire to several buildings being used as dormitories before the suspected growers fled.

When the marijuana operation was discovered, Maine Drug Enforcement Agency officials characterized the size, scope and detail of the operation as quite surprising. They said the plants — many of them 8 feet tall and highly cultivated — were of extremely high quality.

“We have never seen this type of operation in Maine before,” MDEA Director Roy McKinney said in 2009. He confirmed that it was a plantation or farm, where caretakers of the crop lived 24 hours a day, seven days a week.

Martin Roblero, 22, who was granted immunity by federal prosecutors, identified “Moises” as the man who ran the day-to-day operation along with “Scott” and “Rod” at a deposition in May. Velasquez, who testified that he knew the men only by their first names, said that a man named “Malcolm” occasionally visited the grow operation.

The only “Scott” mentioned in court documents was Scott MacPherson, who took his own life in February 2011 just days before he was to have testified before a federal grand jury.

Roblero’s deposition was videotaped so his testimony can be presented to a jury next year. Because he does not speak English, Roblero testified through an interpreter. The witness in March was ordered by an immigration judge to be returned to Mexico. His deportation was delayed so his deposition could be taken.

He was located through DNA samples taken at the grow site that were matched to a man incarcerated in the Midwest, according to court documents. Roblero served a two-year sentence in an Indiana prison on a sex charge. He completed his sentence in March.

When the police raid occurred in September 2009, Roblero said that he along with other Mexican workers, and Moises, Scott and Rod ran for hours from the grow site, which only could be accessed on foot. More than 24 hours after escaping, Roblero said they were picked up by a man, whose name he did not know, in a white van.

Roblero said they were driven to a warehouse where they stayed for two days before being taken to New York and sent on their way. He said the warehouse was full of boxes that contained clothing. Roblero also testified that the unidentified man gave them sweatshirts that had the word “Maine” on them and food.

Berg’s business, Berg Sportswear Inc., located at 852 Dexter Road, and his residence, located at 160 Stetson Road, in Corinna were searched in January 2011 by federal authorities. Search warrants unsealed the following August indicated federal officials were investigating the business that does custom screen printing and embroidery for allegedly using the logos of professional sports teams, distilleries and a motorcycle manufacturer without permission on T-shirts, hats, caps and other merchandise.

No charges related to the illegal use of logos have been filed against Berg or the business.

Under cross-examination in May by French’s attorney, Walter McKee of Augusta, Roblero admitted Tuesday that he had repeatedly lied to investigators during early interviews. He also said that he had false papers to obtain work and did not give the police the correct names of his co-workers, two of whom are relatives.