Christian Gerhartsreiter, 50, who posed as Clark Rockefeller of the storied US family and who is already in prison for kidnapping, allegedly killed John Sohus by battering him to death.
Sohus was last seen in early 1985. Shortly after his disappearance a man calling himself Christopher Chichester, who lived in a guesthouse behind the victim's home in San Marino, northeast of Los Angeles, also vanished.
In May 1994, a body was discovered buried in the backyard of the Sohus family home.
"The remains were later identified as those of John Sohus. An investigation determined he was killed by blunt force trauma to the head," said Jane Robison, a spokeswoman for the Los Angeles County District Attorney's Office.
Deputy District Attorney Habib A. Balian filed a felony complaint seeking the defendant's arrest and extradition from Massachusetts, where he is behind bars for kidnapping, she added.
Gerhartsreiter, who insists he is a Rockefeller, was found guilty in 2009 of kidnapping his seven-year-old daughter and sent to prison for five years.
US authorities say he is a con man who entered the United States more than three decades ago and lived under a series of assumed identities, the latest being Rockefeller, a supposedly brilliant member of the wealthy clan.
The stranger-than-fiction episode began in July 2008 when the German mystery man, seven months after a bitter divorce, snatched his daughter Reigh, nicknamed Snooks, during a supervised visit in Boston.
The ensuing police hunt for the two sparked lurid stories about the suspect's true identity and exploded a fantasy world that had long fooled his wife and acquaintances.
His wife, Harvard Business School graduate Sandra Boss, thought he was a talented and upstanding member of one of America's richest and grandest families.
When they divorced in December 2007, she paid for both their legal fees and gave him 800,000 dollars, two cars and her engagement ring, then left for London with their daughter.