An "potential threat" forced visitors to shelter-in-place at Brookfield Zoo Tuesday.

Approximately 6 p.m., the zoo notified people to remain sheltered till officials cleared the scene.

Approximately 5:15 p.m., 911 dispatchers received a call from a crisis-intervention line threatening the zoo and guests.

The call was described as vague, but Riverside and Brookfield police supervised the methodically clearing the park.

Several hours later, officers cleared public areas and buildings,...

...Despite the call, it was determined that the individual was not within the park at the time.

Approximately 8:10 p.m., Brookfield police and zoo officials gave the all-clear.

There were no further details on the suspect immediately released from the FBI.