Updated

Two South Dakota girls on their way to an end-of-school-year party at a gravel pit in May 1971 drove off a gravel road into a flooded creek and remained hidden until last fall when a drought brought their Studebaker into view, authorities said Tuesday.

State and local officials held a news conference Tuesday afternoon confirming that the 1960 Studebaker unearthed last fall included the remains of Cheryl Miller and Pamella Jackson, both 17-year-olds from nearby Vermillion.

The investigators showed dozens of photographs of well-preserved clothing, a purse and even Miller's driver's license with her smiling photograph.

Attorney General Marty Jackley said classmates who saw the girls before they disappeared and other evidence indicated they had not been drinking. In addition, mechanical tests on the car pointed away from foul play because it was in high gear, he said.

"It's consistent with a car accident," Jackley said.

A fisherman who remembered the 42-year-old case called authorities after noticing one of the car's wheels sticking out of the creek.

The disappearance of the Vermillion High School girls was one of the initial investigations of South Dakota's cold case unit in 2004.

A September 2004 search of a Union County farm turned up apparently unrelated bones, clothing, a purse, photographs, newspaper articles and other items, but not the car.

In a warrant authorizing the search, authorities said that David Lykken, who lived at the farm in 1971 and was a classmate of the girls, might have been involved in the disappearance of Miller and Jackson as well as three other unnamed people. Lykken is in prison serving an unrelated 227-year sentence for rape and kidnapping.

In July 2007, a Union County grand jury indicted Lykken on two counts of premeditated murder, two counts of felony murder and two counts of murder in the disappearance of Miller and Jackson. But state prosecutors dropped all six murder charges after concluding a jailhouse informant apparently lied about Lykken supposedly admitting to causing the deaths.

Union County Sheriff Dan Limoges said Tuesday he had no regrets about the investigation.

"The only unfortunate thing I would add is for the Lykken family, for what they had to go through. But I don't make any apologies for doing our job," he said.

"It's easy to second-guess what could have been done or should have been done," Limoges said. "It just wasn't meant to be until recently."

Family members of the girls attended the news conference but didn't speak.

The girls' remains will be returned to the families for burial.