A federal prison inmate and Johnathan Walkertwo other people were charged Tuesday with conspiring to mail drugs to a penitentiary in California where a mailroom supervisor died last week after opening a letter that prosecutors said was laced with fentanyl and other substances.

According to prosecutors, Jamar Jones, a prisoner at the U.S. Penitentiary in Atwater, California, plotted with Stephanie Ferreira, of Evansville, Indiana, and Jermen Rudd III to send him drugs that he could sell at the prison. They disguised the shipment as “legal mail” from a law office, investigators said.

The penitentiary’s mailroom supervisor, Marc Fischer, fell ill Aug. 9 after opening a letter addressed to Jones that contained multiple pages that appeared to be “soaked,” or coated with drugs, according to an FBI affidavit filed in connection with the charges.

There was no attorney listed in court papers for Jones, who expected to appear in court on the charges next week in Fresno. A number listed in public records for Ferreira did not have voicemail set up. No working phone numbers could be immediately be found for Rudd.