HILLSBOROUGH COUNTY, Fla. -- A suspicious letter with an unknown white substance was discovered on the Mosaic property overnight at 13830 Circa Crossing Dr. on Oct. 1, 2016, according to the Hillsborough County Sheriff's Office.

HCSO have since turned the case over to the FBI, who are investigating what the substance may be.

Mosaic is unsure if it will resume normal business hours on Monday, dependent on the details of the investigation. This investigation comes after the controversy surrounding the radioactive sinkhole that recently appeared near the property.

The Tampa Division of the FBI responded to the scene of the incident following the discovery of the suspicious envelope. The white, powdery substance was sent to a laboratory for further investigation and the results may take several days.

The Hillsborough County Sheriff's Office and the Tampa Division of the FBI are reaching out the public to see if anyone has any further information. Call (813) 253-1000 with further details or information.

Stay with 10News for further details.