ELGIN (CBS) — The FBI is leading the investigation into a threatening letter filled with white powder opened Monday at the Second District Appellate Court building in Elgin.

So far, no one has shown any ill effects, and Elgin Fire Department spokesperson Sue Olafson said tests run by FBI crime lab technicians will take until Thursday evening to complete.

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“The initial testing by the hazmat team ruled out anthrax, risin and botulism,” three potent poisons, she said.

A courthouse clerk opened the letter, which she termed “threatening,” at 11:20 a.m. Monday. The 28 people who were inside the building at the time underwent decontamination by a series of washes and were checked at local hospitals.

Olafson said the letter was sent from a correctional facility in southern Illinois, but so far no one has been charged. She did not divulge specifics about the letter. The FBI is involved in the investigation because it involved the use of the U.S. mail.

She said that the courthouse, at 55 Symphony Way, in Elgin, will remain closed because of the testing until at least Friday.

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