David L. Lykken, 52, who's in prison on an unrelated conviction, told Circuit Judge Steven Jensen that he understood his rights if he pleaded guilty to the new charges but doesn't plan to.
"Yes, your honor, although that will never occur," he said.
Lykken was indicted in Union County on six alternate charges: two counts of premeditated murder, two counts of felony murder and two counts of murder. The maximum punishment for all six counts is life in prison.
He was arrested July 2 at the penitentiary in Sioux Falls, where he's serving a 227-year sentence for a rape and kidnapping conviction in Clay County.
The new indictment charges that Lykken killed Cheryl Miller and Pamella Jackson on or about May 29, 1971, in Union County.
The felony murder counts involve killing during commission of another felony. One count accuses Lykken of killing Miller while raping her. The other accuses him of killing Jackson while committing felony kidnapping, according to the indictment.
The decades-old case was revived in 2004 when the state attorney general's office created a Cold Case Unit, bringing current and former law enforcement officers and other experts together to direct new resources at unsolved crimes.
Lykken appeared in court last week but his arraigned was delayed after he refused to enter a plea and said the proceedings should be in juvenile court.
The judge appointed Mike Butler of Sioux Falls to be Lykken's attorney. Butler plans to file a motion to dismiss the current charges because Lykken was 16 at the time of the killings and juvenile law has since changed.
"It's a substantial matter that needs to be dealt with," he said.
A hearing on that request is scheduled for July 30.