CONRAD, Mont. (AP) - Investigators in northcentral Montana are baffled by a string of cattle mutilations since mid-June, prompting one agency to seek help from a Las Vegas group that studies unconventional theories, including UFOs.

Ranchers in Dupuyer and Fort Shaw have reported four cattle deaths in which portions of the animals' faces were cut or peeled off and eyeballs and genitals were removed.

The animals had not been shot, and investigators say whoever is responsible left few clues behind.

The killings are similar to a string of cattle deaths in the 1970s in the same general area, in which more than 60 cattle in five counties were found mutilated. Those cases remain unsolved, and prompted speculation at the time from some that the deaths were the work of aliens or satanic cults.

Dan Campbell, a deputy with the Pondera County Sheriff's Department, believes humans are responsible, but their motives remain unclear.

"I don't believe in little green men," he said. "I think 500 people have asked me, 'Well, what's doing it?' If I knew, I would get it in the paper."

Colm Kelleher, deputy administrator of the National Institute for Discovery Science in Las Vegas, confirmed Tuesday that the sheriff's office contacted the institute for help.

"They'd heard about some of our previous research from a retired deputy sheriff in that area," he said.

The group describes itself as a research organization that studies a variety of unconventional scientific theories.

NIDS investigated the 1970s cattle mutilations in Montana, and Kelleher said its research found a correlation between the animal killings and UFO sightings around Malmstrom Air Force Base.

"Just because we found a statistical linkage between UFO sightings and animal mutilation, we are not drawing a direct link," he said. "We are completely undecided as to the perpetrators of these mutilations."