SALEM, Ore. (AP) – Authorities suspect the bizarre deaths and mutilations of five bulls in Oregon were caused by humans, but they have no leads.

The deaths of the bulls recall mutilations of livestock across the West and Midwest in the 1970s that struck fear in rural areas. A former FBI agent who headed an investigation said there was no indication that anything other than ordinary animal predators were behind the mutilations.

In the weeks since the dead bulls were found over several days in July, the Harney County Sheriff’s Office has received calls and emails with speculation about what, or who, might be responsible.

Colby Marshall, vice president of the ranch that owned the bulls, says he suspects a cult is behind the killings. Ranch hands have been advised to travel in pairs and to go armed.