A former FBI agent who was involved in the criminal investigation of former Missouri Gov. Eric Greitens turned himself in Monday after being indicted as part of a perjury investigation.

William Tisaby surrendered to authorities on the same day that an indictment against him was unsealed. The indictment charging him with six counts of perjury and one count of tampering with physical evidence was filed under seal Friday in St. Louis Circuit Court.

The indictment alleges that Tisaby lied under oath "about matters which could substantially affect, or did substantially affect, the course or outcome of the Greitens case."

Tisaby, who lives in Trussville, Alabama, was hired last year by St. Louis Circuit Attorney Kim Gardner to investigate allegations that Greitens took a compromising photo of a woman and threatened to share it if she exposed their affair in 2015, a year before the Republican was elected governor.

Gardner's handling of the Greitens case drew strong criticism from his attorneys, who asked police to investigate whether Tisaby lied under oath as part of a deposition of the woman involved in the affair. In June, Mullen appointed Gerard Carmody as special prosecutor to oversee that investigation.

Gardner says she decided to dismiss the case after the judge granted a request by Greitens' lawyers to call her to testify about Tisaby. Gardner said at the time that it put her in the "impossible" position of being a witness in a case she was prosecuting. Despite the dismissal, Greitens, who was also under investigation over other concerns, resigned last June.

Tisaby's attorney, Jermaine Wooten, didn't immediately return a phone message from The Associated Press seeking comment. He said previously that Tisaby is "very upset he's being used as a scapegoat" and described him as "an honest and decent man."

A spokesman for Carmody and a spokeswoman for Gardner said they are unable to comment because of a gag order in the case. Catherine Hanaway, an attorney for Greitens' gubernatorial campaign, didn't immediately return a phone or email message seeking comment.