MORRIS, Ill. (CBS) — Authorities have identified a prison inmate as the person allegedly responsible for sending a suspicious powder to the Grundy County courthouse last month.

As WBBM Newsradio’s Brandis Friedman reports, Grundy County Sheriff Terry Marketti says Wisconsin inmate Bobby L. Coil, 23, was the one who sent a threatening letter with the powder inside to a county judge.

LISTEN: WBBM Newsradio’s Brandis Friedman reports

Five people were taken to the hospital as a precautionary measure after workers in the judge’s office opened the letter on Nov. 21, and discovered the powder.

The letter also prompted a multi-agency hazardous materials response.

Marketti says Coil previously lived in the 600 block of Liberty Street in Morris, Ill., and has done time in the Illinois prison system for nonviolent offenses.

The joint investigation, which included the Chicago FBI Office and the U.S. Postal Service, is expected to lead to federal charges against Coil.

Authorities have not identified what the powder actually turned out to be.

Grundy County is located southwest of Chicago.

The Joliet Herald-News contributed to this report, via the Sun-Times Media Wire.

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