RIVERSIDE, Calif. (AP) — Wildlife rehabilitation experts are working to keep two baby opossums alive after the mother was apparently beaten to death with a sharp rock.

The 2-year-old mother with two babies in her pouch was found in critical condition by a security guard outside an industrial building in Fontana last week, the Press-Enterprise reported (http://bit.ly/1sEUKAP ).

The mother opossum died three days later, said Karolyn Verville, who heads Sunshine Haven Animal Rescue & Wildlife Rehabilitation in Riverside.

Verville has been feeding cat milk replacement to the hungry babies, which she says tends to suit most wildlife.

“We’re the next best thing to mom,” she told The Associated Press on Sunday.

Police in Fontana are searching for the attacker, after a sharp rock with blood and fur on it was found near the opossum.

Animal shelter staff had hoped to save the mother opossum, which had possible skull and jaw fractures, so she could continue to nurse the babies until they were old enough to release into the wild.

Verville said the babies need care for three months before they can be returned to their environment. State law requires animals to be released no more than three miles from the place where they were found, she said.

“The idea is not to protect them from death — nobody can do that,” she said. “It is just to give them a chance at life.”

Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.