Authorities have identified one of the girls seen in a sexually explicit videotape and have showed the images of the other to recognize her.
The tape was turned in to police by a man who said he found it in the desert. It shows a man performing sex acts on a girl around 4 or 5 years old, and shows a girl believed to be 10 to 12 years old appearing in "some kind of peep show," said Nye County sheriff's detective David Boruchowitz.
Authorities hope identifying the girls will help them locate the abuser and rescue them. Still photos of the younger girl, fully clothed, appeared Thursday morning on CBS television's "The Early Show," where Boruchowitz announced that the older girl had been identified.
He said the photos of the younger girl were being released because her life could be in danger.
"She could still be in this situation and (be) abused currently as we speak," Boruchowitz told "The Early Show."
"The easiest way to explain it is if you can imagine the absolute worst things that can happen to a little girl at the hands of an adult male, that has happened and beyond," he said of the video. "It is by far the most heinous and horrible thing that you can possibly imagine on there."
The older girl did not appear to have been sexually abused on the tape and the footage appeared to have been shot from a different room, Boruchowitz said.
Investigators were examining whether the two segments were filmed with the same video camera, he said.
A 26-year-old man, Darren Tuck, surrendered the tape to Nye County sheriff's investigators Sept. 8, after another man reported seeing it, Boruchowitz said.
Tuck told detectives he found the videotape in the desert more than five months ago, although Boruchowitz said the tape did not appear to have been exposed to weather or elements.
Boruchowitz said investigators do not think Tuck made the tape. Tuck was arrested Sept. 19 on charges of promoting child pornography and possession of child pornography, felonies. The top charge carries a possible sentence of up to life in prison.
Tuck was released without bail, pending arraignment Nov. 26, a court official said.
The tape was found near Pahrump, a small town 60 miles (96.6 kilometers) west of Las Vegas.
The Associated Press generally does not identify or release photos of alleged victims of sexual abuse.