Robert N. Clerkin, an airman stationed at Scott Air Force Base in Illinois, has been convicted of stealing Nicolas Cage's $100,000 1989 Porsche 911, reports the Associated Press. Last January, Missouri Water Patrol divers found the vehicle inside the Lake of the Ozarks, submerged in 12 feet of water. The car had been missing for a month after it was stolen from a parking lot in a St. Louis suburb while being transported on a trailer going from California to Pennsylvania. (The driver had stopped in the Midwest to visit his parents during the holidays, PEOPLE.com reported at the time of the car's recovery in January. By then, though, the stereo system had been ripped out before the vehicle was dumped into the lake.) Last week, says the AP, Clerkin, 20, who has already started to serve a six-month sentence in the stockade, was convicted on five charges, including larceny of a military identification card, larceny of the car and conspiracy to steal, destroy and deprive the "Windtalkers" star, 38, of the vehicle, according to Air Force public affairs spokeswoman Lt. Janice Shelley. Clerkin's sentence also includes a rank reduction, forfeiture in pay and a letter of reprimand. In addition, says the news service, authorities have charged Michael J. Grambling, 19, as an accomplice to the theft. His preliminary hearing is slated for July 11.