Brookfield Zoo received a "potential threat" Tuesday, forcing visitors to shelter-in-place for several hours.
In a tweet Tuesday evening at approximately 6 p.m., the zoo asked people to remain sheltered within the facility until officials clear the scene "out of an abundance of caution."
According to Brookfield Zoo Police Chief Mike Pendola, at approximately 5:15 p.m., 911 dispatchers received a call from a crisis-intervention line, with a caller threatening to harm guests and themselves at the zoo.
Information from the call was described as “vague,” but officials instituted a lockdown and worked to methodically clear the park with assistance from Riverside and Brookfield police.
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Officers worked to clear public areas and buildings over the next several hours, but it was determined that the individual was not within the park when the call was made, and there are no active threats at this time.
An "all-clear" was given by zoo officials and Brookfield police at approximately 8:10 p.m.
The FBI is assisting with the investigation, but no further details on the suspect were immediately made available.
The zoo will be open for its normal hours on Wednesday, officials said.