The Bureau of Land Management (BLM) is investigating the deaths of six wild mustangs. Agency helicopter pilots found the animals' carcasses earlier this month during a scheduled round-up of mustangs from a remote area along the Nevada-California border.

Five of the horses appear to have sustained gunshot wounds. The cause of the sixth horse's death is still undetermined, said BLM spokesperson Jan Bedrosian.

Bedrosian would not speculate about a motive for the shooting, but did not rule out the possibility that the incident was connected to controversy over the agency's policy of removing excess horses from public lands.

"We just don't know," she said. "It's against federal law to harass or kill a wild horse on public lands. We're taking this case very seriously