The second floor of the Baltimore City Circuit Court building went into lockdown Monday afternoon after an employee received a letter containing white powder.

The Baltimore City Sheriff’s Office said investigators believed the incident was localized to the second floor of the courthouse, but asked the public to avoid the 100 block of North Calvert Street as the fire department’s hazmat team conducted testing. North Calvert Street was reopened Monday evening.

Authorities say that around 2:40 p.m., an employee on the second floor opened a letter addressed from an inmate at a state correctional facility. The employee contacted the sheriff’s office, which launched established protocols for incidents of this nature.

According to Baltimore City fire officials, three individuals were in close proximity when the envelope was opened. They were isolated and taken to a medical facility as a precaution while further testing is done. Authorities say there is no airborne threat to the facility and any potential exposure is localized to the three individuals, who appear OK.

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Sheriff Sam Cogen briefed Mayor Brandon Scott and courts officials Monday, the sheriff’s office said in a Twitter update.

The sheriff’s office said it is coordinating with the Baltimore Police Department; the U.S. Postal Police; the Bureau of Alcohol, Tobacco, Firearms and Explosives; the FBI; the Maryland Coordination and Analysis Center; and the Maryland Department of Public Safety and Correctional Services. The courthouse’s second floor will remain closed pending the results of the powder analysis.

lillian.reed@thebaltimorebanner.com

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