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ST. LOUIS — A St. Louis grand jury on Thursday indicted Missouri Gov. Eric Greitens on a felony invasion of privacy charge for allegedly taking a compromising photo of a woman with whom he had an affair in 2015. The Republican governor responded that he made a mistake but committed no crime.

St. Louis Circuit Attorney Kim Gardner launched an investigation in January after Greitens admitted to an affair with his St. Louis hairdresser that began in March 2015. He was elected governor in November 2016. Gardner, a Democrat, declined comment beyond a brief news release.

In a statement following the indictment, Greitens was defiant and attacked the prosecutor who brought the charge.

"As I have said before, I made a personal mistake before I was Governor," he said. "I did not commit a crime. With today's disappointing and misguided political decision, my confidence in our prosecutorial system is shaken, but not broken. I know this will be righted soon. The people of Missouri deserve better than a reckless liberal prosecutor who uses her office to score political points."

Greitens' attorney, in a separate statement, called the indictment "baseless and unfounded."

"In 40 years of public and private practice, I have never seen anything like this," attorney Edward L. Dowd Jr. said.

Greitens' legal team immediately filed a motion to dismiss the indictment on the grounds that any relationship with the woman was consensual.

Related: Grand jury investigating Missouri governor’s affair, lawyer says

Reaction from Missouri lawmakers was swift, with some Democrats calling for him to resign and some fellow Republicans also doubtful that he can survive in office.

Republican House leaders said they are launching an investigation of Greitens, which House Communication Director Trevor Fox said is needed before impeachment proceedings could begin.

"We will carefully examine the facts contained in the indictment and answer the question as to whether or not the governor can lead our state while a felony case moves forward," the statement from House Speaker Todd Richardson said. The House has the power to initiate impeachment proceedings against a governor.

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The indictment states that on March 21, 2015, Greitens photographed a woman identified only by her initials "in a state of full or partial nudity" without her knowledge or consent. The indictment said Greitens "transmitted the image contained in the photograph in a manner that allowed access to that image via a computer."

The penalty for first-degree invasion of privacy in Missouri is up to four years in prison.

Greitens was taken into custody in St. Louis and released on his own recognizance, said Susan Ryan, a spokeswoman for Gardner.

In 2015, the woman told her husband, who was secretly taping the conversation, that Greitens took the compromising photo of her at his home and threatened to use it as blackmail if she spoke about the affair. Gardner's news release said it is a felony if a person transmits an image "in a manner that allows access to that image via a computer."

Greitens has repeatedly denied blackmailing the woman, but has repeatedly refused to answer questions about whether he took a photo.

Democratic state Sen. Jamilah Nasheed of St. Louis called for an impeachment process to begin immediately.

"Gov. Greitens has to go," Nasheed said. "Missourians thought they voted for a person of character and integrity, and instead they got a liar and alleged criminal."

Greitens is due in court for his first hearing on March 16, before Circuit Judge Rex Burlison.

Greitens will be allowed to travel. He is scheduled to be in Washington this weekend for a meeting of the nation's governors. It wasn't immediately clear if he would still go.

The indictment came about a month before the statute of limitations would have run out. The statute of limitations for invasion of privacy in Missouri is three years.

Ryan, asked if additional charges could be filed, said the matter is still under investigation. Several lawmakers were questioned last week by investigators from Gardner's office. Kirksville Republican Rep. Nate Walker said investigators talked to him about so-called dark money campaign contributions that are routed through nonprofits to hide their source.

Greitens, 43, is a brash outsider whose resume as a Rhodes Scholar and Navy SEAL officer made him a rising star in Republican politics. He admitted to the affair on the night of Jan. 10, shortly after he delivered the State of the State address to lawmakers.

Greitens emerged the winner in a crowded and expensive GOP primary before defeating the state's attorney general, Democrat Chris Koster, in the November 2016 election to give Republicans control of the governor's mansion for the first time in eight years.

Despite the party's strengthened clout in Jefferson City, there have been frequent clashes between lawmakers and Greitens, who compared them to third-graders and labeled them "career politicians."

He has also faced criticism from some educators and And Greitens' was investigated by for his use of a secretive app that deletes messages.

A former boxer and martial arts expert, Greitens portrayed himself as a maverick during the campaign. He responded to a Democratic attack ad with one of his own in which he fired more than 100 rounds from a machine gun as an announcer declared he'd bring out "the big guns" to fight Democratic policies championed by then-President Barack Obama.

He joined the Navy in 2001 and as a SEAL officer was wounded in Iraq six years later. He also served as a White House fellow, founded a nonprofit organization for veterans and authored a best-selling book.

His charity, The Mission Continues, faced scrutiny during the campaign when Democrats accused him of insider politics for accessing the donor list to raise about $2 million through its top contributors.

Greitens and his wife, Sheena, have two sons, Joshua and Jacob.