Transcript for Indiana murder mystery seemed similar but not linked to Iowa cold case: police
Tonight the grieving grandfather of one of the two teenage girls murdered in a small Indiana community. Pleading with the public to help bring her killer to justice. Police have been circulating an image and voice recording of the potential suspect. Captured on one of the victim's phones, just before her murder. Here's ABC's Alex Perez. She loved taking pictures of anything and everything. Reporter: These woods of delphi, Indiana, now a crime scene. We're a small, close-knit community, so this hits very hard. Reporter: This community still on edge after the horrific murder of two young teens. I think it's terrible. It makes me sick to my stomach. It made me sick going to the bridge, thinking, one of my friends died down there. Reporter: Investigators piecing together the last moments of the two girls. This horrible crime has torn a hole in our families that will never heal. Reporter: Friends and family shattered by the sudden loss. Down the hill. Reporter: Tonight, a killer still at large. This voice and photograph, possible clues. Authorities say, recorded on the victim's phone that fateful February day. It's around 1:00 P.M. On Monday, February 13th. A family member drops the girls off for a hike. Authorities believe the girls walked through this nature trail and about an hour after they started their hike, they ended up right here on this railroad bridge. At 2:07 P.M., they upload this photo of Abigail walking across the train tracks over this bridge. That would be their last communication. Less than an hour later, the teens are scheduled to be picked up, but they never show. They started looking for them, around 5:00. Got law enforcement involved. Reporter: Hundreds of volunteers involved, police checking Snapchat pictures for clues. Liberty's grandfather speaking. Missing, abducted, we don't know for sure. Cell phone has been pinging around town. Describe that search, the volunteers, this is something that really impacted the community. It did, it did. We had, estimating, well over 200 to 300 volunteers. Then of course the emergency responders, which included law enforcement, local firefighters. We searched well into the night and the early morning hours. Reporter: But the next day, detectives discover their bodies, three-quarters of a mile from that very bridge seen in liberty's last Snapchat. This is rural Indiana. Most of the people that are born and raised here stay here. It is very uncommon for that to happen in a small community. It's not something that you get here. Reporter: A community heart-broken. Now to think something could have happened here in our own town, it's scary. I think everybody is just ready to know what happened and why and who did this. Reporter: Two families, reeling. It's the small things that seem to hurt the most. It's just natural to holler for them to come to dinner, or in the mornings to get up and get ready for school. Then, expect them to come through the door after school. The silence, when we don't hear their voice. Reporter: Officers combing through thousands of tips. Authorities not revealing information about how the teens died, but releasing this chilling audio they believe to be the killer. Down the hill. Down the hill. We think there's enough there that somebody would recognize that voice, and we want that person to call us. It's always easier to crack a case earlier, witnesses are fresh, you're getting tips early on and you hope the person might still be in the area. Reporter: Investigators hunting for this man who they call a suspect. Down the hill. Reporter: Authorities revealing this audio and image came in liberty's phone in her last moments, managing to hit record. She's a hero, she had the presence of mind, she didn't feel comfortable and turned on her video camera. Hope that those will lead to a tip and then an arrest. As poor as this picture is, somebody knows. If you're watching, we'll find you. Reporter: The public has the potential to be the best ally in this investigation. Do you know that guy? Do you recognize the voice? Do you know someone who looked like him, who was in the area? Anything they can get is helpful. This morning, liberty German's grandfather, appealing to the public for help. However small it may seem, it is extremely vital to capture every tip we can get. Please, we need your help. Reporter: As mystery still clouds delphi, Indiana, 400 miles away, a father in Iowa hoping this case could help lead to answers in his own daughter and niece's abduction and murder. Everything just started coming back to me, thinking about what the parents are and the family are going through. And just what I had gone through, and my family's gone through. All those things just come back to you when you see one of these cases. Reporter: On July 13th, 2012, 8-year-old Elizabeth Collins and her 10-year-old cousin lyric cook, went for an afternoon bike ride and never returned. The last five days have seemed eternal. Yeah, just like forever. Every day is like, we're like, when is it going to end? You know. When is it going to end? When is this nightmare going to end? Reporter: Their bicycles were recovered on this trail next to a small lake after they were reported missing. Whoever is out there, we're just begging you to bring our girls back home. Reporter: The bodies of those two girls were found five months later. Elizabeth's father points out the eerie similarities with L libthe other murders. Both crimes committed on the 13th of the month. Two kids at once is a very uncommon thing to have happen. And also just being on the 13th of the month, just kinda struck me as really odd. Reporter: The authorities hunting liberty and Abigail's killers telling ABC news they've compared notes with investigators in Iowa. At this point, we're not comfortable saying, yes, there is a connection, or no, there's not. We just don't have enough information. Reporter: On the surface, these cases have similarities, underage kids, on trails, remote areas of two different states, killed during daylight hours. Once you get beyond that, the cases really aren't similar. You have an abduction in the one in Iowa, and you also have a number of states in between these two crime scenes. And so the idea that it's the same guy, I think, is not likely. Reporter: Still as communities grieve in two separate states, the family is holding on to hope for answers. One of the biggest advantages of talking about this Iowa case now, publicly, is that when cases get publicized, people do come forward. Reporter: Tributes scene across delphi over the last month, for these bright girls taken too soon, as a community waits anxiously for an arrest. For "Nightline," I'm Alex Perez in delphi, Indiana.
This transcript has been automatically generated and may not be 100% accurate.