Police speak directly to the unknown Delphi killer: 'Today could be the day -- sleep well'

In Delphi, Indiana, a close-knit town of nearly 3,000 residents, this weekend marks five years since its most haunting event -- the slayings of two eighth-grade girls on a local hiking trail -- a devastating crime that stripped families of their innocence and thrust the rural community into a murder mystery that remains unsolved.

Feb. 13, 2017 was an unusually warm day in Delphi, about 70 miles north of Indianapolis, and best friends Abby Williams, 13, and Libby German, 14, were enjoying a day off from school.

They headed to the trail -- and never made it home.

There appears to be substantial evidence in the case -- from audio and video footage of the suspect to a new lead from social media -- but no arrest has been made. Police are also not willing to disclose key facts about the crime, such as the cause of death, which experts interviewed by ABC News say is unusual.

They also say that the benefit of continued secrecy and pursuing cryptic leads in the case may have passed.

Nonetheless, five years on, the families still say they have faith in the head of the Indiana State Police, Doug Carter, who said he urges them to continue to hold his feet to the fire.

"We know a lot about you ... today could be the day -- sleep well," Carter said in a direct message to the killer.

Watch the full story on "Nightline" TONIGHT at 12:35 a.m. ET on ABC.

'Our own little bubble'

Libby was outgoing and competitive, excelling in softball, soccer, swimming and volleyball. But she also stood up for the underdog, her grandmother and guardian, Becky Patty, told ABC News.

"She made an impression on people with her kindness," she said.

Abby was independent, artistic and musical, said her mother, Anna Williams.

"She was one of the most helpful kids I've ever had the pleasure of being with," her mom said. "She loved helping other people … assisting her nieces, playing games."

The inseparable friends spent their last night alive having a sleepover at Libby's house, Becky Patty said. There was no school on Monday, Feb. 13, so the girls slept in and had pancakes.

"We were in our own little bubble," Becky Patty said.

When Abby and Libby didn’t come home from their afternoon at the trail, Libby's grandfather, Mike Patty, went to look for them.

By nightfall, the girls were still missing and he called the police. Officers and neighbors descended on the streets and trails with flashlights, he said.

Williams said, "We couldn't find anything on any form of social media saying that they were planning on hanging out or anything with people ... the only logical reasoning for them not to be here is that neither of them had a good sense of direction and they're lost and somebody's hurt."

The next day -- Valentine's Day -- the girls' bodies were found near the trail.

Video, a recording and a sketch

The murders cast fear across Delphi, with parents keeping their kids inside and once-friendly neighbors looking at each other with suspicion.

In 2017, authorities released a grainy image of the suspect, who they say was on the trail the day the girls went missing. In 2019, police released a brief video clip -- footage taken from Libby's phone -- showing a grainy image of the suspect walking on the bridge near where the girls were last seen.

Police also publicized the suspect's voice -- a recording of him saying "guys ... down the hill" -- which was recovered from Libby's phone.

Authorities in 2019 released a new suspect sketch that officials said was based on a witness' recollection of what he or she saw.

Despite all that evidence, no arrest has been made.

Two Indiana State Police detectives work full-time on the case, investigating alongside local authorities and looking into all tips and leads that come in, state police spokesman Sgt. Jeremy Piers said.

Carter, the Indiana State Police superintendent, told ABC News this week, "My resolve to catch him is as strong now as it is Day One."

"I get 25 to 30 tips a week personally," he said. "I can assure you -- it's moving."

A deepening mystery

So much remains a mystery. Most significantly, how Abby and Libby died has still not been released to the public. The state police spokesman would only say that's because "there is some information about this case that we cannot release to protect the integrity of the investigation."

"One day I'm gonna be able to explain it -- we will be able to explain why we held certain things," Carter said.

Speaking directly to the killer, he added, "we know a lot about you," though he didn't elaborate.

Though police routinely withhold details from the public when working to identify a suspect, ABC News contributor and former FBI agent Brad Garrett said that he thought the lack of disclosure of the particular aspects of the cause of death is strange.

"It's odd to me that they have not released what caused Abigail and Libby's death, because it's fairly routine ... for the public to at least generally know what happened," he said.

Garrett said the cause of death having a unique aspect that only the killer would know is the only logical reason he can think of for law enforcement withholding the information.

Robert Ives, the chief prosecutor in Carroll County at the time of Abby and Libby's murders who has since retired, thinks the time has passed to keep the cause of death a secret.

"I would like to hear an explanation from those leading the investigation what benefit is gained with secrecy," Ives told ABC News.

Two months ago came a new lead -- but that's also shrouded in mystery.

State police announced in December that, while investigating Abby and Libby's case, they "uncovered" a fake Snapchat and Instagram profile called "anthony_shots," where the unknown user took photos of a known male model and communicated with underage girls "to solicit nude images, obtain their addresses, and attempt to meet them."

The user of the "anthony_shots" profile, which was active in 2016 and 2017, "portrayed himself as being extremely wealthy and owning numerous sports cars," police said.

The male model in the photos has been identified and isn't a person of interest, according to police.

Authorities won't say if Abby or Libby communicated with the fake profile.

Carter was tight-lipped on the "anthony_shots" investigation, saying the profile has "generated a tremendous number of leads for us -- and that’s as far as I can go."

In a statement this week state police said they're urging anyone who communicated with, met or tried to meet the "anthony_shots" profile to contact law enforcement.

Mike Patty said he sometimes gets criticized for being so supportive of law enforcement. He admitted he gets frustrated, saying he "never thought we'd be here five years and not have resolution."

But Mike Patty's still supporting the police, because, he says, "who else is gonna make the arrest for me?"

"What's the most effective way to get this done? It's to support them, right?" he said.

"Obviously I don't know everything they [the police] have," he said. "And they're not gonna roll those cards out on the table at this point in time."

"Our job is to get the information out there," he continued. "'Cause one day we're gonna get ahold of the right person. Or they're gonna hear our plea for their help enough that they're finally gonna say something."

Williams agreed.

"It did feel we do have more information than a lot of cases have," she said. "I'm not saying that the cops are in error --- law enforcement has done us well ... the thousands and thousands and thousands of hours that they have put into our case is frustrating for everybody."

Carter said, while having conversations with Mike Patty, "There's things he wants to know that we haven't told him. Can you imagine? I can't. He's looking at a man that knows the answer to a question he's asking about the death of a grandchild. And I won't tell him."

"I want them to continue to hold us to the fire," Carter said of the families.

'We always have hope'

Those middle-schoolers enjoying a warm day in the fresh air would now be young adults finishing their freshman year of college. Williams said Abby "would've turned into a really good young lady."

Becky Patty said she made a vow to Libby to never give up on finding her killer and to "live our life making her proud."

"We live our life like she would want -- she was way more giving and she was way more forgiving than the rest of us," Becky Patty said.

"We include her every day in our life," she continued. "She's just not physically standing here, but she's here. So we just don't let her be gone."

Mike Patty said he's still hopeful for an arrest.

"We always have hope," he said.

"So if you know and you're not saying something, I encourage you to do so, 'cause ... this guy could strike again," he said. "I don't want it to happen to anybody else."

Anyone with information can submit a tip at abbyandlibbytip@cacoshrf.com or 765-822-3535.

ABC News' Jenn Leong, John Kapetaneas, Kelsey Klimara and Jenner Smith contributed to this report.