ATWATER, Calif. (KMJ/KFSN) -- The investigation into the death of an employee at U.S. Penitentiary Atwater has led to charges against three people, including one inmate.

On August 9, correctional officer Marc Fischer became sick after coming into contact with a substance in the mail room, according to the Bureau of Prisons. Fischer was taken to the hospital, where he died. Loved ones have said he was close to retirement at the time.

The U.S. Attorney's Office has now filed multiple drug-related charges against USP Atwater inmate Jamar Jones, as well as Stephanie Ferreira of Indiana and Jermen Rudd III of Missouri.

The charges include "Conspiracy to Distribute and Distribution of a Controlled Substance, to wit Methamphetamine, "Spice", and Fentanyl."

Prosecutors say Jones and Ferreira had Rudd mail a letter to Jones that was laced with drugs and fraudulently labeled as legal mail. Officials say Jones was supposed to sell the narcotics in the prison.

35-year-old Jones is set to make his first court appearance in Fresno next week, while 35-year-old Ferreira and 37-year-old Rudd will be arraigned in the states where they live.

Jones and Rudd face a maximum of 30 years in prison and a fine up to $250,000. Ferreira faces a maximum penalty of 20 years in prison and a fine up to $250,000.