Trophy hunter Walter Palmer killed Cecil the lion earlier this month after the big cat was allegedly lured out of the Hwange National Park boundaries.
Two people involved in the hunt have appeared in court in the southern African nation on poaching charges, and furor continued to grow on American soil with calls to punish Palmer too.
The US Fish and Wildlife Service said it had opened a probe into the hunt.
But Palmer remained out of the public eye, as crowds left plush toys of lions, tigers and monkeys at his River Bluff Dental practice in Minnesota.
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A sign reading "Rot in Hell" was plastered on the office door.
A Minnesota congresswoman joined calls to investigate the dentist, a seasoned hunter with a poaching conviction over the 2008 killing of a black bear in the United States.
"To bait and kill a threatened animal, like this African lion, for sport cannot be called hunting, but rather a disgraceful display of callous cruelty," Betty McCollum said Wednesday.
Meanwhile, Safari Club International, an international hunting organization that Palmer belonged to, said it also supported a probe and that it had revoked his membership.
"SCI has imposed immediate emergency membership suspensions of both the involved hunter and his guide/professional hunter, and they will remain in place pending the outcome of an investigation," the group said in a statement.
Cecil was a popular attraction among many international visitors to the Hwange National Park and was part of a University of Oxford research project.