Updated

MADISON, Wis. (AP) — A Wisconsin judge has appointed a special prosecutor to determine whether criminal charges should be filed against nine University of Wisconsin-Madison researchers and officials responsible for experiments that killed sheep.

The experiments concerned an illness known as decompression sickness, or "the bends," which can occur during deep-sea diving. The sheep are exposed to compressed air in a high-pressure chamber and then the air pressure is decreased.

Wisconsin law prohibits anyone from killing an animal through decompression.

Dane County Circuit Court Judge Amy Smith appointed the special prosecutor after two animal rights groups filed a petition seeking criminal charges. She says numerous sheep have died in experiments since 1988.