Wichita ? Two of six people facing drug charges in a case that led to the shooting death of Greenwood County Sheriff Matt Samuels pleaded guilty Monday and agreed to testify against the man accused of Samuels’ murder, the U.S. attorney’s office said.

Darrell E. Cooper, 43, of Madison, pleaded guilty to one count of conspiracy to manufacture methamphetamine; one count of manufacturing methamphetamine; one count of establishing an operation to manufacture methamphetamine; and two counts of possessing a firearm while using a controlled substance.

Rhonda O’Brien, 37, of Madison, pleaded guilty to conspiracy to manufacture methamphetamine and using a communication to facilitate a drug trafficking crime.

Samuels was killed Jan. 17 while trying to serve a search warrant at a home in Greenwood County. Scott Cheever, 23, is charged in the sheriff’s death and the government is seeking the death penalty against him. Prosecutors say Cheever shot Samuels to protect a meth lab.

Cooper and O’Brien are scheduled to be sentenced Jan. 9.

Two other defendants, Belinda Cooper and Billy Nowell, pleaded guilty in September to federal drug and weapons charges and are awaiting sentencing.

A fifth defendant, Matthew D. Denny, 23, of El Dorado, was acquitted of first-degree murder in state court but convicted of conspiracy to manufacture meth. Prosecutors say he was a lookout while meth was manufactured in the Coopers’ home.