The petition was started on July 28 and currently has over 140,000 signatures.
White House Press Secretary Josh Earnest said the petition has “reached the threshold” that would warrant a response but did not offer a time frame. He did note that decisions about prosecution and extradition are made at the DOJ.
The U.S. Fish & Wildlife Service, which has offered assistance to Zimbabwe in its investigation, has asked Palmer to contact them "immediately."
"The U.S. Fish & Wildlife Service is investigating the circumstances surrounding the killing of 'Cecil the lion,'" the agency told ABC News in a statement today. "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."