Police investigating the murder of two girls in Indiana have released a video clip from one of the victim’s phones.
In the audio from the recording, the words, “down the hill”, can be heard in a deep voice.
Investigators said they hoped releasing the footage would result in someone recognising the person's voice, who is believed to be the main suspect.
Liberty German, 14, and Abigail Williams, 13, were reported missing after they did not return from a hike in Carroll County, Maryland.
Their bodies were located in the woods about three-quarters of a mile from an abandoned bridge where they had been dropped off the day before.
Investigators believe the recording was made as criminal behaviour was about to take place and it is thought other evidence had also been recovered from the phone.
"Libby had the presence of mind to turn on her video camera," Indiana State Police spokesman Capt. David Bursten said. He also described Liberty as a "hero", ABC news reported.
Indiana State Police also released a photograph of their primary suspect, who was spotted on a nature trail around the time the two teenagers disappeared.
It is unclear if the voice in the audio belongs to the man, who was photographed in blue jeans, a blue jacket and a hoodie.
Authorities have offered a $41,000 (£33,000) reward for any information leading to an arrest.
