McAfee and Indiana State Police Superintendent Doug Carter appear in a video posted on McAfee's Twitter account Wednesday in which they appealed to the public for tips and said the reward fund was being raised by $97,000, to $200,000.
Fourteen-year-old Liberty German and 13-year-old Abigail Williams were found dead Feb. 14 in a wooded area near Delphi, which is about 60 miles northwest of Indianapolis. They had gone out hiking the day before.
McAfee urged viewers to review a photo and audio clip of a male saying "down the hill" that police say came from German's cellphone.
In the audio clip, a male voice can be heard saying three words: "Down the hill."
The audio was posted on the Indiana State Police website.
Authorities say that audio clip was retrieved from Libby's cell phone.
Investigators revealed they have other video and evidence that was recovered from her phone as well. That evidence is not being released.
Investigators say it is unclear to them whether the voice heard in the audio clip is the same person seen in the still image of the suspect that officials have been circulating, or possibly another suspect.
"The audio quality is not superb, but there is enough there that someone can recognize the voice," said Indiana State Police Captain David Bursten.
Indiana State Police Sergeant Tony Slocum praised Libby for having the presence of mind to record what was happening during that horrifying situation.
"This young lady is a hero. There is no doubt. To have enough presence of mind to activate the video system on her cell phone to record what we believe is criminal behavior that is about to occur," he said.
Was this a chance encounter or did the suspect target the girls?
Bursten says all options are being investigated, adding this crime was one of two things.
"That was a chance encounter... or that person knew that they were going to be there," he said.
Authorities spent a big part of the press conference delivering an impassioned appeal to the public to call in tips to help nab the person or persons responsible for the murders.
Investigators believe someone out there that recognizes the suspect can be the key to capturing him.
"Even with technology we need human intelligence, and we need you," said Indiana State Police Superintendent Doug Carter.
"Somebody knows. And if you're watching, we'll find you," Carter said, addressing the suspect.
They have set up both a phone line and email address for tips:
WLS-TV contributed to this report.