DELPHI, IN – Within days of releasing a chilling recording, investigators have received thousands of tips about the deaths of two Indiana teenage girls.

On Feb. 13, a relative dropped off Liberty (Libby) German, 14, and Abigail Williams, 13, so they could spend the day hiking. But the girls never showed up to the location where they were supposed to meet another relative later that day.

Their bodies were found near Deer Creek near Delphi, about 60 miles northwest of Indianapolis.

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The Victims: Abigail Williams and Liberty German

Last Monday, authorities named a man seen in photographs walking along the trail around the time the girls were dropped off as the main suspect in their deaths.

On Wednesday, authorities released a video clip retrieved from the cellphone of one of the victims, 14-year-old Liberty German.

On the recording, a man’s voice can be heard saying “Down the hill.”

“Libby had the presence of mind to turn on her video camera,” said Indiana State Police spokesman Capt. David Bursten. “There’s no doubt in our minds that that young lady is a hero.”

While authorities have not disclosed how the girls died, they are treating the deaths as a double-homicide.

“Someone knows who this individual is,” said Indiana State Police Superintendent Douglas Carter. “And if you’re watching, we’ll find you.”

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Man police call the main suspect in girls’ deaths.

According to ABC News, investigators said it is possible more than one suspect is involved and it’s unclear if the voice in the recording belongs to the man in the photographs.

ABC News also reports the FBI is helping local investigators and the FBI Director James Comey has been briefed on the case twice.

Investigators said they have recovered other recordings and evidence from German’s cellphone, but that information is not being released.

Anyone with information about the man or about the investigation should call the Carroll County Sheriff’s Department at 765-564-2413, the Delphi Police at 765-564-2345 or the Indiana State Police at 765-567-2125. Callers can remain anonymous.