Photos from the scene

Watch News 4 coverage

(KMOV) -- According to zoo officials, a threat was made against the St. Louis Zoo.

A bomb threat was called in around 8:30 a.m. on Friday.

Officials evacuated parts of the Zoo so that police and security could search the buildings.

Bomb-sniffing dogs were brought in to aid in the investigation.

It took four hours to search the area.

Nothing suspicious was found, but police are investigating where that threatening phone call originated.

The zoo itself was not evacuated.

Zoo officials said, based on advice from the police, they didn't try to evacuate the entire zoo because they wanted to avoid people panicking and bolting for the exits.

An estimated 14,000 people were at the zoo on Friday.