A researcher who studied a beloved lion who was killed by an American dentist in Zimbabwe claims in a new book that the animal suffered for many hours after he was initially shot with a crossbow. A portion of Oxford University biologist Andrew Loveridge's new memoir "Lion Hearted: The Life and Death of Cecil and the Future of Africa's Iconic Cats," was published in National Geographic.

In the excerpt, Loveridge writes that judging by data sent from Cecil the lion's GPS collar, he was killed almost 10 to 12 hours after he was initially wounded.

"Cecil suffered incredible cruelty for at least 10 hours, severely wounded and slowly dying," Loveridge writes.

The 2015 death of Cecil, a well-known and protected lion, sparked outrage around the world. He was killed by Walter Palmer, a dentist and big-game hunter from Minnesota. After the incident gained international attention, Palmer issued a statement saying in part "I had no idea that the lion I took was a known, local favorite, was collared and part of a study until the end of the hunt. I relied on the expertise of my local professional guides to ensure a legal hunt."

However, Palmer pleaded guilty in 2008 for making false statements to the U.S. Fish and Wildlife Service about a black bear he fatally shot in western Wisconsin. Palmer had a permit, but shot the animal outside an authorized zone, then tried to pass it off as being killed elsewhere, according to court documents.

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Conservationists previously reported that the men involved in Cecil's hunt tied a dead animal to their car to lure the lion out of a national park.

In the excerpt from Loveridge's book, he writes that the Zimbabwean professional hunter who accompanied Palmer "panicked" when he first saw Cecil's collar, but removed it and hung it from a tree, instead of handing it over to officials. Loveridge also writes that his research team only realized something was wrong six days later, when they noticed Cecil's collar hadn't transmitted data.