JACKSON HOLE, WYO \u2013 UPDATE (11:48am, January 18):\u00a0Some of the 52 released bison from the Stephens Creek facility have been located in the Mammoth area. Investigators working on this case have confirmed that bison were intentionally released by unknown individuals when pens were broken into and damage occurred to government property.\u00a0 Yellowstone had planned a bison roundup beginning January 16 that would involve a closure to the public of the Stephens Creek facility. When they got there, park officials discovered someone had beat them to it. On the morning of January 16, park staff discovered 52 bison being held at the Stephens Creek facility for quarantine had been released from their pens. In response, the National Park Service has initiated a criminal investigation of this incident. \u201cThis is an egregious criminal act that sets back bison conservation. It delays critical ongoing discussions about a quarantine program and the transfer of live Yellowstone bison to tribal lands. The park is aggressively investigating this incident,\u201d said Yellowstone National Park superintendent Dan Wenk. Currently, park staff is making an effort to locate and recapture the bison. None of the animals have yet been located. The missing bull bison were being held in two separate pens. A group of 24 animals have been in confinement since March 2016 and another group of 28 animals has been confined since March 2017. These animals were being held and tested for brucellosis at Stephens Creek as part of a plan being considered to establish a quarantine program. Some of the animals were targeted for tribal use. "I am absolutely heartbroken for the Fort Peck Tribes who have been working with the park, the state of Montana, and Animal and Plant Health Inspection Service for years to repatriate these bison," said Interior Secretary Ryan Zinke. "The criminals who broke into a national park facility to release these bison put at risk the safety of the animals that are now at risk of being culled and our park rangers who are rounding them up. I will be working with Secretary Perdue to see if we can get back on track to transfer the brucellosis free bulls to the tribe this year." The Stephens Creek facility is now closed permanently to the public. Anyone with information about this incident is encouraged to call the Yellowstone National Park Tip Line at 307-344-2132 or online.