A missing South Carolina restaurant lobbyist apparently shot himself in the head, leaving behind a suicide note referencing a federal probe into as much as $900,000 missing from the association he managed, police said.

The body of Tom Sponseller, who disappeared more than a week ago, was discovered Tuesday morning by investigators inside a double enclosed room in the lower level of a parking garage near his office in Columbia, according to authorities.

Richland County Coroner Gary Watts said during a press conference Tuesday that it appears Sponseller, president and CEO of the South Carolina Hospitality Association, suffered a "self-inflicted gunshot wound to his head." A 9-mm. handgun was recovered at the scene.

An official autopsy is under way as authorities investigate the circumstances surrounding his death, Watts said. He added that it appears Sponseller died "instantaneously."

Columbia Police Chief Randy Scott said a note penned by Sponseller was found by his co-workers, who broke into a locked desk drawer in his office Tuesday. The handwritten letter referenced a federal probe into missing funds at the association he headed, Scott said. Packaging from a gun was also discovered inside the drawer.

Two sources familiar with the three-page note told the State newspaper that Sponseller said he was aware of the missing money and the federal probe. He said he was sorry it had happened while he was in charge of the association, the sources said.

Federal authorities investigating Sponseller's disappearance acknowledged this week that they were looking into several hundred thousand dollars missing from the association.

Law enforcement officials reportedly said that Sponseller's accounting director, Rachel Duncan, 41, is a person of interest in the missing money investigation, which involves allegations of "gambling."

"Ms. Duncan has been interviewed, and she is a target of our financial crime investigation," U.S. Secret Service Special Agent in Charge Michael Williams told the newspaper.

Sponseller, 61, was last seen Feb. 18 by co-workers at his office in downtown Columbia. He was reported missing by his wife later that night after friends and family tried repeatedly to contact him by phone.

Sponseller's Mercedes sedan was found parked in the garage near his office and no signs of a struggle were evident. His cellphone and wallet were missing.

Duncan had no comment Friday when approached by Fox News outside her home in Lexington.

A family friend who answered the door at Sponseller's home last week said she did not believe the money investigation was related to his disappearance.

Sponseller is a Citadel graduate and a former Air Force officer, according to his biography on the South Carolina Hospitality Association's website.

He has been lobbying for the state's hospitality and tourism industry for more than 20 years. He is married and has three adult children, all of whom have worked in the hospitality industry, according to the bio.

Fox News' Mary Quinn O'Connor contributed to this report.