Zimbabwe's wildlife minister says extradition is being sought for Walter J. Palmer, the Twin Cities big-game hunter and dentist implicated in the killing of Cecil, a prized research lion in Zimbabwe.

Oppah Muchinguri, environment, water and climate minister, told a news conference Friday: "We want him tried in Zimbabwe because he violated our laws. ... Police should take the first step to approach the prosecutor general who will approach the Americans. The processes have already started."

"Unfortunately it was too late to apprehend the foreign poacher as he had already absconded to his country of origin," Muchinguri said. "We are appealing to the responsible authorities for his extradition to Zimbabwe so that he be made accountable."

Muchinguri noted the worldwide attention the case has received.

"There has been an outcry," she said. "Almost 500,000 people are calling for his extradition and we need this support."

Meanwhile, U.S. wildlife authorities have opened an investigation into the killing of Cecil, and said Thursday, and again on Friday morning, that they have been unable to contact Palmer, the Twin Cities big-game hunter and dentist implicated in the fatal hunt.

Officials of the U.S. Fish and Wildlife Service said that, even though the African lion is not protected under U.S. law, they share Zimbabwe’s interest in protecting threatened animals. “The investigation will take us wherever the facts lead,” said Edward Grace, the agency’s deputy chief of law enforcement.

Separately on Thursday, the head of Zimbabwe’s safari industry association told the Star Tribune that he believes bribery was involved in the hunt because Palmer’s guide did not have proper hunting licenses and permits.

“There had to be [bribes],” said Emmanuel Fundira, president of Zimbabwe’s Safari Operators Association. “The documents which they used for carrying out the hunt were all illegal and fraudulently obtained.”

Fundira, who has assisted government officials in investigating the incident, also said he believes it is “highly, highly likely” that Palmer will be charged by Zimbabwe authorities, though he added that Palmer “probably committed the offense unknowingly.”

Palmer’s guide, Theo Bronkhorst, already has been charged in the killing, and the owner of the farm where the hunt took place, Honest Trymore Ndlovu, is expected to be charged next week. “I would recommend [that Palmer] get in touch to put his side of the story in before assumptions and or conclusions are arrived at,” Fundira said.

Authorities seeking Palmer's extradition have described him as an accomplice to the illegal hunt. But they have not specified what charges might be laid against him, meaning it is unclear what penalty he could face if he is tried and convicted.

‘Deep regret’

The killing unleashed a firestorm of outrage that has spanned the globe. Palmer suspended his dental practice this week as critics tied up his phone lines, filled his social media account with harsh postings and staged a passionate protest Wednesday outside his Bloomington office.

Eden Prairie police said Thursday that they are keeping watch on Palmer’s neighborhood but not providing him personal protection.

Palmer’s whereabouts on Thursday were unclear. Protests subsided at his dental practice, but reporters and curious onlookers did gather outside his Florida vacation home, a $1 million property on Marco Island.

Palmer declined to comment when reached by the Star Tribune on Wednesday and did not answer his phone when called Thursday morning. Earlier in the week, he issued a statement saying that he felt deep regret over the incident. He said that he had no idea at the time that he was shooting a prized lion and that he believed his guides were acting legally.

The exact nature of the U.S. investigation remains unclear. African lions are not listed under the core U.S. wildlife protection statute, the Endangered Species Act. A second law, which bans the import of wildlife killed under illegal circumstances, would not come into play because Palmer did not try to bring the lion’s carcass home, lawyers say. A third U.S. statute forbids bribery of foreign officials by Americans traveling overseas, but attorneys said this week it’s not clear if that law would come into play.

Federal officials said this week that they are cooperating with their counterparts in Harare, Zimbabwe’s capital, and that the U.S. has a broad and flexible extradition treaty with Zimbabwe, though it is designed with an eye to combating organized crime, terrorism and drug trafficking.

The treaty obliges both countries to extradite any individual from either country who is charged with or convicted of an offense punishable by both countries by at least one year in prison.

Jeff Flocken, the North American regional director for the International Fund for Animal Welfare, in Washington, D.C., said he would be surprised if Palmer were extradited.

“Typically, wildlife crimes don’t rise to [that] level of scrutiny and prosecution,” he said, noting that the U.S. allows the legal import of nearly 450 African lion trophies each year.

Flocken noted that U.S. hunters are responsible for about 60 percent of African lions killed each year for sport.

The U.S. Department of Justice does not track how many people are extradited from the country for environmental prosecutions such as wildlife trafficking. But the number would appear to be small. In recent years, the U.S. has extradited just 54 to 72 fugitives a year, including U.S. and foreign citizens under all categories, a Justice Department spokesman said.

The killing of Cecil and Palmer's involvement reached President Obama's doorstep Thursday, when presidential spokesman Josh Earnest said a petition on the White House's "We the People" website had topped the 100,000 signatures needed to trigger a response from the administration.

Earnest said the White House would, indeed, respond. He added during his daily briefing that "this is an issue that is a particularly important policy issue in Africa. ... This is something that we are obviously aware of."

Richard Chibuwe, deputy chief of mission at Zimbabwe's embassy in Washington, D.C., applauded the Zimbabwe wildlife minister’s statement.

“This is pure poaching,” Chibuwe said. “The guys new exactly what they were doing. There is absolutely no excuse for what they did.”

Calls from ordinary Americans as well as Zimbabwe nationals expressing outrage over the lion’s killing have been pouring into the embassy, Chibuwe said, and staff are trying to answer as many of the calls as they can.

Palmer should come forward, Chibuwe said.

“If he is innocent.. why should he be hesistant to appear before the court?” he said. “He should have a sense of responsibility.”

Chibuwe said he doesn’t think the extradition process has been initiated yet, and that it likely would be handled between the two countries’ justice departments.

Wildlife minister Muchinguri accused Palmer of "a well-orchestrated agenda which would tarnish the image of Zimbabwe and further strain the relationship between Zimbabwe and the USA."

Zimbabwe and the United States have often sparred over the years. The southern African country has blamed its economic woes on U.S. sanctions against President Robert Mugabe and close associates, though many commentators have attributed Zimbabwe's economic decline to mismanagement.

Washington imposed the penalties on Zimbabwe because of human rights concerns. More broadly, Mugabe has long railed against what he calls Western meddling in Africa, saying it is an extension of the colonial rule of the past.

Outfitter is a no-show

In Zimbabwe on Thursday, a magistrate conducted the second of two court hearings on Cecil’s killing, amid signs that prosecutors were still trying to sort out charges against Palmer’s guide and outfitter.

Ndlovu, owner of the farm where the hunt began, was supposed to appear in a regional court in Hwange, about 435 miles west of Harare, but prosecutors at the last minute said they weren’t prepared to file charges. Ndlovu’s attorney said charges are expected by next Wednesday.

Zimbabwe’s top wildlife regulator said this week that the kill was illegal because Bronkhorst, the guide, lacked the proper hunting permit for a lion kill for 2015. The charge was repeated by prosecutors at his hearing on Wednesday.

Many conservationists had predicted that Ndlovu and Bronkhorst would be charged with poaching, which can be punished by a fine of up to $20,000 or a 10-year prison sentence.

Bronkhorst was charged instead with failing to prevent the killing of Cecil, and lawyers said Thursday that a poaching charge was inappropriate for the guide and outfitter, but possibly appropriate for Palmer.

Fishing without a license

Palmer, 55, an avid trophy hunter and bow-and-arrow marksman, shot and wounded the lion with a compound bow about July 1 during a guided nighttime hunt outside of Hwange National Park. After tracking led them to the wounded lion about 40 hours later, the hunting party finished it off with a gunshot.

The lion lived in the national park, where it had protected status. It had been collared as part of a long-term study and had became a favorite among tourists from all over the world.

Palmer had been listed in a record book compiled by Safari Club International, an organization for big-game hunters. The club’s record book listed 43 kills by Palmer, all by bow and arrow, including moose, buffalo, a polar bear and a mountain lion. The club said this week that it was suspending the memberships of Palmer and his Zimbabwe-based guide.

Palmer has run afoul of the law at least twice over the years, with a guilty plea and fine in 2008 for misleading federal authorities about a bear he killed illegally in Wisconsin and a misdemeanor for fishing without a license in Minnesota’s Otter Tail County.

 -- The Associated Press contributed to this report.