Chicago Police are investigating the deliberate release of 15 police horses from stalls inside their barn on Sunday night.
Two horses were injured in the incident, with one of them, named J.R., apparently suffering chemical burns to his face after being sprayed with a fire extinguisher.
Another mounted, named Schott, suffered a cut to his right back leg and had another injury to a hoof.
Officers working on Sunday evening had left the stalls in the grounds of the South Shore Cultural Center around 9.45pm. They returned about 11.15pm to find the animals loose.
The burglar or burglars responsible had apparently entered through a window.
Inquiries are continuing.