COLUMBIA — A Marietta man and two others have pleaded guilty in federal court in Anderson to conspiracy to distribute oxycodone and other controlled substances, a violation of Title 18, United States Code, Section 846, according to the U.S. Attorney’s Office.

Nathan C. Johnson, 51, of Marietta, Patricia T. Brookshire, 54, of Travelers Rest, and Carmen B. Crudo, 31, of Hendersonville, N.C., entered their pleas before Senior U.S. District Judge G. Ross Anderson Jr., who will impose sentence after he has reviewed the presentence report prepared by the U.S. Probation Office.

U.S. Attorney Bill Nettles said that evidence presented at the change of plea hearing established that the federal Drug Enforcement Administration had undertaken a long-term investigation into the distribution of oxycodone in the upstate of South Carolina.

On July 8, 2014, agents conducted a controlled purchase of 25 oxycodone pills from Cheryl Shipman, who pleaded guilty earlier this year, using a confidential source. To fulfill the order, Shipman traveled to meet Johnson and was observed conducting a drug transaction with Johnson.

Further investigation revealed that, in addition to Johnson, Shipman had other sources of supply for Oxycodone and that she sold oxycodone to area dealers and addicts on a daily basis. Carmen Crudo frequently traveled from Hendersonville, North Carolina, to purchase pills from Shipman.

According to reports from Henderson County, North Carolina, Crudo was arrested on April 24, 2014, after she was observed selling oxycodone obtained from Shipman to a known drug user. Patricia Brookshire’s role in the conspiracy was to provide Shipman with methadone for resale.

On July 10, 2014, Shipman purchased 99 methadone pills from Brookshire. This transaction was recorded by law enforcement.

Nettles said the maximum penalty the defendants can receive is a fine of $250,000 and/or imprisonment for 20 years, plus a special assessment of $100.

The case was investigated by agents of the federal Drug Enforcement Administration. Assistant U.S. Attorney Bill Watkins of the Greenville office handled the case.