Taylor Placker, 13, and Skyla Whitaker, 11, were found June 8 alongside a country road in Weleetka, about 75 miles from Tulsa.

On the tape, a breathless woman can be heard saying: "Somebody killed two young girls. They are both down here dead. My granddaughter and her friend. ... Help me. Please!" CNN reported. The caller is identified only as a member of the family.

Jessica Brown, an Oklahoma State Bureau of Investigation spokeswoman, said investigators had run down about 500 leads and eliminated scores of suspects. Police said they are looking for two gunmen.

"Someone has to come forward," she said.