CONNERSVILLE, Ind. — A man has been charged with manslaughter in the death of an Indiana teenager who was last seen in 1986, authorities said Thursday.

The Fayette County sheriff's department identified the man as Shawn McClung.

Denise Pflum, an 18-year-old high school senior, disappeared after telling her family that she was returning to the site of a bonfire where she had misplaced her purse the previous night.

"The information and probable cause alleges that McClung previously claimed that Pflum was still alive, but has recently admitted that he killed her in March of 1986," the sheriff's department said in a statement.

"No further comments will be made at this time, as the investigation is ongoing regarding the involvement of other parties," the department said.

Online court records show McClung, 55, pleaded not guilty during a court appearance. Bond was set at $500,000. Defense attorney Jud McMillin declined to comment.

McClung was Pflum's former boyfriend at the time she disappeared, her mother, Judy, told NBC's "Dateline" in March.

Pflum's family thanked investigators Thursday with a statement posted on Facebook.

"Our daughter was a special person whom we will never forget, and we know that this community will not forget," the family said. "We are so grateful for all of those who have followed her story, who have helped with the investigation and who have shown support and love."

Judy Pflum said Denise had planned to attend Miami University in Ohio.

"She had everything going for her," Judy Pflum told "Dateline." "If she were here today, she'd be working on a cure for cancer. Or, well, maybe even a cure for this coronavirus. She just wanted to help people."