Investigators with the South Dakota Division of Criminal Investigation and other agencies recently began searching the gravel pit in northwest Iowa, according to an Associated Press report.
Sara Rabern, spokeswoman for the South Dakota Attorney General's office, said the search is linked to the investigation of an unsolved 1971 case but she could provide no other details.
The gravel pit is across the state line east of a rural Alcester farm where David Lykken, 52, lived as a child. Investigators searched that place in 2004 as part of a cold case unit investigation into the disappearance of two Vermillion girls.
A six-count indictment charges that Lykken, who is now in prison for an unrelated crime, killed Cheryl Miller and Pamella Jackson on or about May 29, 1971, in Union County.
The 17-year-old Vermillion High School juniors were last seen that day driving a Studebaker Lark on rural road on their way to a party.
Lykken was 16 years old at the time.
The six alternate murder counts against him all carry a maximum punishment of life in prison.
Lykken was arrested July 2 at the penitentiary in Sioux Falls and pleaded not guilty July 16 in Elk Point. His next court hearing is scheduled for July 30.