TUCSON - An anonymous donor has added $1,000 to the reward for information leading to an arrest in the case of 80 bats found dead or dying under a Tucson bridge last month.

Arizona Game and Fish Department officials say the bats were shot with a BB gun. The agency is offering a $750 reward for information leading to an arrest in the case.

Game and Fish officials said Wednesday that the $1,000 reward is being donated by someone with the Arizona Land and Water Trust.

Rabies and other diseases were ruled out by lab tests along with exposure to magnesium chloride, which was used by city workers to de-ice the Speedway Bridge on Dec. 23. The dead bats were found days later.