Note: we are republishing this story, which originally made the news in February 2016.

Wildlife experts partially solved the mystery behind the death of 13 bald eagles, but they still don’t know who the culprit responsible is.

The eagles, some who were so young that they still hadn’t grown their white head feathers, were poisoned by carbofuran, a deadly

According to Cornell Lab of Ornithology, the pesticide is so deadly that a single granule is enough to kill a small bird. The use of the liquid pesticide on food crops was banned by the Environmental Protection Agency in 2009.

However, according to toxicologist Karyn Bischoff of Cornell University’s Animal Health Diagnostic Center, many people may still have aging containers of the pesticide in their sheds.

In February 2016, a man looking for deer antlers on Maryland’s eastern shore stumbled upon four of the 13 dead bald eagles. He called the Maryland Natural Resources Police, who investigated the Federalsburg site and discovered nine more dead birds.