Citizen Sleuths Spring Into Action in Indiana Murder Mystery as Reward Reaches $50G

Playing Audio Of Suspected Killer In Indiana Teens' Murder Has Triggered A Thousand Tips

America is a nation of detectives as everyday citizens attempt to identify a suspect featured in cell phone video of the two murdered teens in Indiana.

Read: Did Murdered Indiana Teens Capture the Voice of Their Killer?

The grainy image and haunting audio of the man saying "down the hill" were recorded by 14-year-old Liberty German on her cell phone.

German and her best friend, Abigail Williams, 14, were found murdered near a creek on a popular hiking trail in Indiana on February 13. 

People in the town of Delphi — population 3,000 — say they refuse to believe the suspect is one of their own.

"Somebody knows this voice," one Delphi citizen told Inside Edition. "Somebody has to know who this guy is. We are begging you, begging you to come forward. We need to find out who has done this to our girls."

The release of the audio has triggered more than a thousand tips. Citizen sleuths, including Nancy Grace, are offering their theories about the killer.

"We hear that muffled: 'down the hill, down the hill' — Why was it muffled?" Grace told ABC News. "Because I think she put it in her pocket. Now they are only releasing a portion of it, why? It could be an attack on the girls. It could even be their murders that they are not releasing to spare the families. But there's more proof on that video!"

A source familiar with the investigation described the full cell phone recording as "the stuff of nightmares."

The reward for information leading to the arrest of the suspect has been increased to $50,000 following a $9,000 donation by the office of U.S. Congressman Todd Rokita, according to police. 

There are several intriguing theories police are working on, including the possibility of two killers. It's a theory that may explain why one of the girls wasn't able to get away while the other was murdered.

Read: Police Name Mystery Man Caught on Surveillance as Suspect in Murders of Teen Hikers

Another proposed theory involves whether the killer lives nearby, as he appears to know the woods and back roads.

An additional idea centers on whether the killer was recently released from prison.

Veteran New York Homicide Detective Sergeant Joe Giacalone is following the case

"I don't think this is the first time he has done something like this," he told Inside Edition. "He was following them for a while and I think that's why she was able to snatch this picture because if you notice he's looking down he's not even paying attention. She realized maybe there's something wrong and she snapped this blurry video.”

Watch: How a Social Media Photo May Have Tipped Off Predator That Killed Girls on Hike