DELPHI, Ind. (AP) — Police believe one of the two teenage girls killed last week in Indiana recorded the voice of a suspect in their deaths.

Indiana State Police released a clip of a man’s voice saying “down the hill.”

During a Wednesday news conference, Capt. David Bursten said the audio came from 14-year-old Liberty German’s cellphone.

Authorities say Liberty also captured an image of a man walking near the hiking trail outside Delphi about the time she and 13-year-old Abigail Williams disappeared Feb. 13.

“To have the presence of mind to activate the cell phone to record criminal behavior. There’s no doubt that young lady is a hero,” said Indiana State Police Sgt. Tony Slocum.

Police said there is more audio that has not been released.

The teens’ bodies were found the next day in a rugged wooded area off the trail.

Abigail Williams (left) and Liberty German (right) (Credit: Facebook)

Abigail Williams (left) and Liberty German (right) (Credit: Facebook)

Bursten said investigators aren’t certain the voice was that of the photographed man who investigators who have called their main suspect.

The police tip line for the case is: 844-459-5786.

Twenty FBI agents have joined State Police to investigate a crime that has stunned this community 126 miles southeast of Chicago.

“Why Libby. Why Abby. Why Delphi. Why Carroll County?” said State Police Supt. Douglas Carter, struggling to compose himself. “This is a classic example that evil lives amongst us.”

The FBI wants to talk to people who suddenly missed work or canceled meetings on Feb. 13, the day the girls were reported missing.

The reward in the case is now up to $41,000.