Federal prosecutors have taken over the case against two local men who are accused of conspiring to sell large quantities of drugs in the Keene area.

Roland Leison Farnsworth III, 36, of Keene and Ronald J. Karvosky Jr., 42, of Marlborough were arrested in September following a months-long investigation by Keene police.

On Wednesday, a federal grand jury in Concord charged the two men with conspiracy to distribute cocaine base, also known as crack cocaine, and fentanyl.

Farnsworth and Karvosky are accused of conspiring to sell at least 40 grams of fentanyl, which triggers a mandatory minimum prison sentence of at least five years if they are convicted.

Both had been charged with drug-related offenses in Cheshire County Superior Court after their arrest. A county prosecutor dropped those charges late last week because of the pending federal prosecution.

Federal sentences are often longer than state sentences in drug cases.

The Keene Police Department’s investigation of Farnsworth goes back at least to June, when a robbery was reported at his Roxbury Street residence, according to affidavits written by Detective Jennifer M. Truman. Keene police determined drugs had been stolen from the apartment, though Farnsworth denied the robbery was drug related, Truman wrote.

Farnsworth later moved to 158 Church St. Police surveilled the home between June and September, observing various people stopping by for a few minutes at a time, “which is indicative of drug trafficking,” Truman wrote. The visitors, according to Truman, included people known to use or sell drugs.

Police also heard sources “repeatedly” mention Farnsworth’s name in connection with drug activity, according to Truman, including two sources who said they had bought drugs from Farnsworth on different occasions. One person claimed Farnsworth was the “big dealer” in Keene, selling drugs to most of the city’s drug users, Truman wrote.

Over the summer, at the direction of Keene police, confidential informants bought heroin/fentanyl or crack cocaine from Farnsworth on multiple occasions, Truman wrote. The alleged sales varied in value from under $60 to $800.

At least one source told Keene police that Karvosky regularly traveled to Massachusetts to pick up drugs for Farnsworth, and officers observed Karvosky’s vehicle coming and going from Farnsworth’s address, according to Truman’s account.

In late August, the detective wrote, a judge authorized police to place a GPS tracker on Karvosky’s vehicle. The tracker showed the vehicle making frequent trips to the same address in Methuen, Mass., then heading back to Keene after a few minutes, Truman wrote.

After one such trip in early September, police observed Karvosky pulling into Farnsworth’s driveway with Farnsworth in the passenger seat, Truman wrote. A person cooperating with Keene police bought $800 worth of suspected heroin/fentanyl from Farnsworth the same night, according to the detective’s affidavits.

Police arrested the two men Sept. 14 at the Church Street home as they returned from another trip to Methuen, Truman wrote. A woman in the car with them said the group had driven to the Massachusetts city, where Karvosky had a drug connection that Farnsworth also used, according to one affidavit.

After his arrest, Truman wrote, “Farnsworth admitted he sells drugs to a lot of people in the Keene area in a lot of different quantities” and said he and Karvosky traveled south to pick up drugs several times a week. Farnsworth said the two men had bought a combined $2,000 worth of crack cocaine and heroin, with his share being $600 and the rest belonging to Karvosky, according to the affidavit.

Karvosky declined to speak to police.

On searching the car, police found more than 20 grams of crack cocaine and just over 40 grams of heroin/fentanyl, Truman wrote. Farnsworth also had on his person crack cocaine and $1,360, mostly in 20-dollar bills, according to the affidavit.

After a detention hearing Monday, Karvosky was released on bail. Farnsworth remained in detention pending trial.

Paul Cuno-Booth can be reached at 352-1234, extension 1409, or pbooth@keenesentinel.com.

Follow him on Twitter

@PCunoBoothKS.