Thirteen bald eagles were found dead in a field. This is what killed them.

The 13 bald eagles were found lifeless on a Maryland farm more than two years ago, many with wings splayed, bodies intact, and talons clenched. Several were too young to have their species' distinctive white heads. And at least six, according to a federal lab report, had ingested a highly toxic pesticide that has been essentially banned from the U.S. market, in part because it is lethal to birds.

The report, which was obtained by the Annapolis, Maryland, radio station WNAV and shared with The Washington Post, answers one big question in a mysterious wildlife crime that angered conservation organizations and stumped U.S. Fish and Wildlife investigators, who were involved because the bald eagle is a federally protected species. Tests showed that the birds were poisoned, as officials suspected. What remains unsolved is who did it.

"There was no smoking gun," said John LaCorte, a special agent for the U.S. Fish and Wildlife Service who spent six months interviewing more than a dozen landowners and property managers in the Eastern Shore area where the eagles died. "It's very frustrating."

The chemical that killed the birds, carbofuran, came under scrutiny three decades ago for killing what the Environmental Protection Agency estimated were as many as 2 million birds a year, threatening the bald eagle's then-fragile road to recovery. The granular form, which a Fish and Wildlife official in 1987 told The Post was the primary cause of death for bald eagles in the Chesapeake Bay region, was banned in the mid-1990s. The EPA disallowed the use of liquid carbofuran on food crops in 2009, saying the residue posed an unacceptable safety risk. Environmental groups hailed the decision as a victory for human health and for wildlife.

Today, the pesticide is off the market, and the bald eagle is no longer endangered, though it is protected by the Migratory Bird Treaty Act and Bald and Golden Eagle acts. But carbofuran still occasionally kills birds and other wildlife in the United States - sometimes intentionally, and sometimes as collateral damage after an animal scavenges a poisoned carcass.

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In November, a Montana farmer was fined $1,000 for killing a bald eagle that fed on a calf carcass he had injected with carbofuran in a bid to kill coyotes; it also killed three coyotes and a hawk. Last June, a Pennsylvania man was fined $3,500 after sending Furadan, the brand name carbofuran was previously sold under, to workers at his New York farm and instructing them to pour it on sheep carcasses to kill hawks that had preyed on his lambs. It killed two red-tailed hawks, a rough-legged hawk and two bald eagles. A Wisconsin father and son were each ordered to pay more than $100,000 in 2014 after killing more than 70 wild animals, including bald eagles, as they targeted wolves and coyotes with carbofuran.

California authorities recently raised alarm about the widespread use of carbofuran at illegal marijuana grow sites. Mourad Gabriel, a wildlife biologist who has documented that trend, said in an interview that the chemical is usually found in Spanish-labeled bottles, suggesting illegal importation.

"They're not using it as a pesticide . . . they're using it as a rodenticide to kill the animals that will come and eat the plants," U.S. attorney McGregor Scott told reporters in Sacramento in May. "This is a game-changer, because it's a lethal poison."

Carbofuran is an acute toxin, which means it can kill after a single exposure, or an exposure of a short duration. And it doesn't take much. Farmers in Africa have used it to kill lions that eat livestock.

Karyn Bischoff, a toxicologist at Cornell University's Animal Health Diagnostic Center, recently examined a dog that had been fatally poisoned by it in the Caribbean. "It's a pretty ugly way to die," said Bischoff, whose lab sees carbofuran poisoning cases every year or two. The chemical can cause diarrhea, vomiting, seizures and excessive salivation, she said; it can also cause glands in the lungs to secrete fluids, causing animals to "drown in their own fluids."

Robert Edgell, 89, owns the property of more than 100 acres outside Federalsburg, Maryland, where the eagles were discovered in February 2016. He had just gotten out of his truck when he stumbled upon the first carcass, which he described this week as a "young, immature eagle." Walking on, he found two more dead eagles and then, nearby, a fourth standing upright with its tail feathers seemingly stuck in the ground. It looked as though it had been stuffed, he said.

Others were discovered in the same area by a man Edgell said he'd allowed to look for deer antlers on the property. Federal officials who came to investigate collected them all - 13 total - as well as a partial raccoon carcass and fur found nearby. Killing just one bald eagle is punishable by up to two years in prison and a fine of $250,000.

"I was dumbfounded," said Edgell, a retired state trooper whose farm has been in his family since 1910. "Usually you see one or two soaring over the place, but to see 13 in that area and all deceased. . . . In all my years, I'd not seen anything like this."

Six of the bald eagles were sent to the U.S. Fish and Wildlife Forensics Laboratory in Oregon, which determined that all had carbofuran in their stomachs, crops or both. All had consumed a "recent meal," states the report, which was obtained via a Freedom of Information Act by WNAV reporter Donna Cole. Five of the six had eaten raccoon, and some had eaten deer or chicken; the sixth had dined on marsh rice rat, but the report notes that any of the birds could have vomited other stomach contents.

The lab also examined the raccoon carcass and fur. It could not determine cause of death, but carbofuran was detected on both samples. LaCorte said investigators believe the birds fed on the carcass of the raccoon, which may have been the target, and then perished.

"Bald eagles don't normally predate on raccoons," Gabriel said, because the latter are primarily nocturnal, and eagles do most of their hunting during the day. "The raccoons probably succumbed to the carbofuram and they were out there decomposing and the bald eagles capitalized on the tainted meat."

Although carbofuran can no longer be purchased, there's probably plenty of it still out there, Bischoff said.

"A lot of people have an old shed somewhere that's got all this stuff in it that has been sitting there for 40 years," Bischoff said. "They may or may not know it's there."

Edgell, who grows soybeans and wheat on about 70 acres of his property, said he appeared before a grand jury in U.S. District Court in Baltimore, where he was questioned about the eagle deaths. Fish and Wildlife investigators also questioned him and his farm managers, including about chemicals used on the farm. Edgell said this week that neither he nor his employees had ever used carbofuran.

LaCorte said he believes Edgell did not use the chemical on his property. It's possible, he said, that one eagle picked up the raccoon carcass elsewhere and then carried it to Edgell's property, where other eagles also consumed it.

But even if eagles weren't the targets, someone illegally used the carbofuran, and in doing so added a particularly egregious case to what LaCorte called an "epidemic on the Eastern Shore" of wildlife poisoning crimes. A separate 2016 case, in which five bald eagles were poisoned in Delaware, remains under investigation, officials said.

"It's every year where we get a couple of poisonings," LaCorte said. Poisoning a nuisance animal or predator, rather than trapping it or building a fence, is "the cheaper and easier way out," he said. The cases are hard to solve, LaCorte said, because there are usually few to no witnesses - or none willing to talk. "If anyone wants to see things get done about this, they need to be courageous and come forward," he said.

Edgell said the eagles' deaths disturbed his friends, and he assured them he was upset, too.

"It was certainly nothing done on the farm that killed them. It's something else," he said. "I love to see eagles flying. They're a beautiful bird."