The Rockefeller impostor convicted of the cold-case murder of a California man has asked to represent himself at sentencing. Christian Gerhartsreiter made a brief court appearance Thursday to make his request. His lawyers were on the phone from Boston. Los Angeles County Superior Court Judge George Lomeli delayed sentencing from June 26 to Aug. 15. Gerhartsreiter has been represented by Boston attorney Jeffrey Denner, along with his law partner, Brad Bailey. A jury found that Gerhartsreiter, who lived briefly in California in the 1980s, killed John Sohus, a 27-year-old computer programmer who was the son of the defendant’s landlady. Sohus and his new wife, Linda, vanished in 1985. No trace of her has been found.