An activist ecological organization has upped the reward to $7,500 for help nabbing the killer of an endangered California wolf wearing a tracking collar.

The yearling male, identified by researchers as OR-59, was discovered killed by a bullet on a county road in the far northeast region of the state in December 2018. The wolf had traveled to California from Oregon late that year. He was fatally shot just days after a rancher spotted him feeding on the carcass of a calf that had died of natural causes. Wildlife officials have been unable to crack the case.

There were early leads that have since been exhausted, so the U.S. Fish and Wildlife Service decided to broaden our inquiry by seeking information from the public by offering a reward of $2,500, agency representative Pam Bierce told the Capital Press on Friday.

This loss is a terrible blow to wolf conservation in California, Amaroq Weiss of the Center for Biological Diversity said in a statement . It underscores why our endangered wolves need the strongest possible protection at both state and federal levels. The organization has added $5,000 to the reward.

The wolf is one of several dozen illegally shot along the West Coast over the last few years, according to the center.