Palmer issued a statement about the lion's killing.
"I hired several professional guides, and they secured all proper permits," Palmer said in the statement. "To my knowledge, everything about this trip was legal and properly handled and conducted."
Palmer claims that he didn't know that the lion was famous, The Star Tribune reported.
"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," Palmer said.
Officials from the Zimbabwe Conservation Task Force claim that Cecil, who was 13 years old, was lured out of the national park with bait and was shot by Palmer with a crossbow. The day after the hunt, Cecil was found wounded by hunters and was killed before being beheaded and skinned, The Telegraph reported.
USA Today reported that the lion's GPS collar, which was being tracked by an Oxford University research program, was removed.
Cecil was known to visitors to Hwange National Park and seemed to enjoy contact with humans, The Telegraph and other media outlets have reported in recent days.
Johnny Rodrigues, the task force's chairman, said Theo Bronkhorst and Honest Ndlovu, a hunter and private game park owner respectively, will face poaching charges.
Rodrigues said Palmer paid Bronkhorst and Ndlovu more than $50,000 to hunt the lion.
Palmer said he has yet to be contacted by Zimbabwean or American authorities.
Palmer is described by the Associated Press as an avid hunter who pleaded guilty in 2008 to making false statements to the U.S. Fish and Wildlife Service about a black bear he shot and killed in Wisconsin.