The mysteriously dead 13 bald eagles that were found on Maryland’s Eastern Shore last month were likely killed by humans, officials say. The event remains the biggest die-off of bald eagles in the state in 30 years. Necropsies ruled out diseases and natural causes. Investigators have ruled out poisoned animal carcasses from a nearby farm. U.S. Fish and Wildlife Service spokeswoman Catherine J. Hibbard said the investigation is now focused on human suspects, but declined to disclose more information about how the birds died. The bald eagle, the national animal of the United States, is a protected species. Killing one is a crime punishable by up to a year in prison and a $100,000 fine. Authorities are offering a $25,000 reward to help find whoever killed them.