DENVER -- Actor Woody Harrelson's father, Charles Harrelson, died in the Supermax federal prison where he was serving two life sentences for the murder of a federal judge, officials said Wednesday.

Charles Harrelson, 69, was found unresponsive in his cell on March 15 and apparently died of natural causes, said Felicia Ponce, a Bureau of Prisons spokeswoman in Washington.

Ponce did not know the cause of death. Fremont County Coroner Dorothy Twellman did not immediately return a call.

Charles Harrelson was convicted of murder in the May 29, 1979, slaying of U.S. District Judge John Wood Jr. outside his San Antonio, Texas, home. Prosecutors said a drug dealer hired him to kill Wood because he did not want the judge to preside at his upcoming trial.

Charles Harrelson denied the killing, saying he was in Dallas, 270 miles away, when Wood was killed.