Former NFL player raises reward to 'catch monster' in teen girls' killings The amount was increased to $200,000 for tips about their deaths.

 -- The desperate search for a killer in the slaying of two Indiana teen girls has gotten a boost.

Former Indianapolis Colts punter Pat McAfee and team owner Jim Irsay are nearly doubling the reward for information leading to an arrest of the perpetrator. The amount was increased to $200,000 for tips about the killings.

"The only people that are really going to know who this is, is somebody who’s had a long relationship with this person, whether it's family or friends or something like that, and they're probably struggling with loyalty right now,” McAfee said today on “Good Morning America” of someone who might know the killer. “But this is a horrible person.

"And we thought that $200,000 is a life-changing amount of money. Hopefully, we just spread the word across the country, find this monster, get him off the street, which would be good for America, good for Indiana, just good for everybody."

On Feb. 22, police released evidence of a video clip retrieved from the cellphone of one of the victims. When police played some audio from the clip at a news conference in the town of Delphi, reporters heard just three words from a deep voice: "Down the hill."

The rest of the video will not be released at this time because of the ongoing investigation. Investigators recovered other evidence from the girl's phone that is also not being released, Capt. David Bursten said during a February news conference.

Police also released a photograph of a man who is the primary suspect in the investigation.

Indiana State Police Sgt. Tony Slocum spoke out this morning on "GMA," saying authorities are still investigating as the manhunt intensifies.

"We have officers out shaking the bushes, so to speak, knocking on doors investigating or speaking to suspects or anybody we believe might have evidentiary information to help us solve this case," Slocum said. "That's why what Pat and Mr. Irsay had done is so important to what we're doing here in Delphi, Indiana."

McAfee, the former Colts player, said he has plans to travel to Delphi and meet the victims' families.

"I think we're going to catch the guy and I can't wait to get up there and celebrate that," he said.

People can provide information about this case by calling the Delphi murder tip line at 844-459-5786. Information can be reported anonymously. Tips can also be emailed to abbyandlibbytip@cacoshrf.com.

ABC News' Morgan Winsor, Alex Perez and Andrew Fies contributed to this report.