Mar 10, 2016:

The U.S. Fish and Wildlife Service said they have determined that the 13 eagles found dead last month were killed by humans.

Eastern Shore eagles didn't die of natural causes, authorities say | The Baltimore Sun

Maryland officials search for killer of 13 bald eagles found in field | The Guardian

Feb 22, 2016:

Two days ago, thirteen bald eagles were found dead in a field on a farm in Caroline County, Maryland.

In a press release entitled "Ten Thousand Dollar Reward for 13 Eagles Found Dead on Eastern Shore, Maryland" the U.S. Fish and Wildlife Service, along with The Humane Society of the United States, The Humane Society Wildlife Land Trust, and The Phoenix Wildlife Center, Inc. are, together, offering a reward of $10,000 for information leading to the arrest and conviction of suspected offenders.

Thirteen bald eagles were found dead on a Maryland farm | The Washington Post