The U.S. Fish and Wildlife Service is looking for the man who shot Cecil the lion, and he is not returning their calls.
Dr. Walter Palmer became the subject of international attention—and the target of criticism—when it was revealed that he allegedly shot an adult male lion near a national park in Zimbabwe. Zimbabwean authorities have already arrested Palmer's hunting guide and the owner of the land where the lion was shot, after details suggested the hunt may have been illegal.
Edward Grace, deputy chief of law enforcement for the Fish and Wildlife Service, sent the following statement to CNBC:
"The U.S. Fish & Wildlife Service is investigating the circumstances surrounding the killing of 'Cecil the lion,' " the statement read. "That investigation will take us wherever the facts lead. At this point in time, however, multiple efforts to contact Dr. Walter Palmer have been unsuccessful. We ask that Dr. Palmer or his representative contact us immediately."
Attempts by CNBC to contact Palmer also met with no success. Palmer's hunting activities have landed him in legal trouble in the past. He was given a year's probation and fined $3,000 for the illegal killing of a black bear in Wisconsin in 2006, according to NBC News.
Read MoreCecil the lion: Does killing lions help save them?
The hunters allegedly lured the cat out just beyond the borders of the Hwange National Park in Zimbabwe, using a dead animal as bait. Palmer then shot it with a bow and arrow and the group tracked it for several hours before finally killing it with a bullet to the head, officials said.
They then took the lion's head and skin, both of which have since been confiscated as evidence in Zimbabwe, according to Johnny Rodrigues, chairman of the Zimbabwe Conservation Task Force. The animal wore a GPS collar because it was part of an ongoing study sponsored by Oxford University.
Both the guide and the landowner appeared in court in Zimbabwe Wednesday to face poaching charges.
Palmer, a dentist from Minnesota who is fond of big game hunting around the world, has apparently traveled back to the United States. He issued a statement to the Star-Tribune of Minneapolis through a spokesperson saying he had believed the hunt was legal and that he regretted killing the lion. The paper said on Tuesday that Palmer was in the Twin Cities area, but he left his local dental practice, River Bluff Dental, closed as of Wednesday.