Riley said the girls' bodies were found in a wooded area about 50 feet from the banks of Deer Creek in an area less than a mile upstream from the railroad bridge.
An FBI team remains at the crime scene collecting evidence.
Riley said there are no suspects but police have received hundreds of leads. He said they are not releasing the girls' cause of deaths yet, citing the ongoing investigation.
"The investigation is still in its baby steps, so to speak, and we don't want to put that information out yet," he said during a news conference in Delphi. Carroll County Sheriff Tobe Leazenby said authorities do not yet have a suspect or suspects in the girls' slayings. He said the teens' deaths are very upsetting for residents in the city of about 3,000 residents that is the county seat.
Leazenby and Riley urged the public, particularly people who were hiking Monday in the area where the girls went missing, to contact police with any tips they might have to help authorities in the investigation.
"We're going to get to the bottom of this. We feel confident. And we're going to do everything within our resources to reach justice in this situation," Leazenby said.“I shot back. I got him," the clerk told Regan.
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He thanked volunteers who helped search the base of the bridge and surrounding trails for the girls, whose bodies were found by one of those volunteers.
Riley said a relative of one of the girls dropped them off Monday near the bridge and another relative had agreed to pick them up later. He said the girls went hiking Monday because the school they attended did not have classes that day.
Riley said the girls planned to hike a local trail, and authorities have received no information suggesting they planned to meet anyone else on that trail.
He said authorities are urging local residents to use caution, keep track of their children and report anything unusual to authorities while the criminal investigation continues.
"There's somebody out there, somewhere. We don't know if it's a person who came in and left, or if it's somebody in the neighborhood," Riley said.
The Associated Press contributed to this report.