Cecil the lion killer Walter Palmer could face up to 10 years in jail if he is convicted in a Zimbabwean court.
The country has called on the US to extradite the 55-year-old dentist after it emerged he had shot the protected animal with a bow and arrow.
Palmer fled the country before the Zimbabwean authorities knew what had happened.
He admits killing black-maned Cecil, who was a tourist attraction, but said he hired professional guides and believed he had the necessary permits.
The life-long hunter has gone into hiding since his identity was revealed by Zimbabwean conservationists.
American philanthropists have pledged to match new donations up to $100,000 to the research team who had been tracking Cecil since 2008.
Dozens of protesters gathered outside the practice of a suburban Minneapolis dentist who killed a protected lion in Zimbabwe.
A host of celebrities have taken to social media to speak out on the killing of well-known lion Cecil in Zimbabwe by a US dentist.