Officials of the Bureau of Land Management and a wild horse protection group joined Friday in urging an informant to contact them about the slaughter of 450 Nevada mustangs.

Dick Wright, chairman of the Washoe County Secret Witness program, said a person called a few days ago indicating he or she had information on the horse kill and wanted to speak to authorities."They never called back," Wright told a news conference. "We believe this witness has information that could be crucial to this case."

Wright urged the person to call back Secret Witness, which he said hasn't been receiving many other tips about the slaughter discovered two months ago.

"We assure them they will remain anonymous," he said.

Bob Stewart, public information officer for the BLM, announced that the Department of Interior added $5,000 to reward money for any person who provides information leading to the arrest and prosecution of the horse killers.

The total reward offered now is $17,000, including money from the Humane Society and other animal protection groups including the state Commission for the Preservation of Wild Horses.

Discovery of the slaughter began in August with the helicopter siting of 41 carcasses in the Austin area. The discoveries have spread over 102,000 acres in central Nevada's Lander County and now total 450.

Investigators say the killings apparently began about two years ago, though some of the horses were shot late this spring or early this summer.

Stewart, who refused to release details about any leads or suspects in the case, said investigation has been difficult because the shootings are spread over such a vast area.