Richard Allen charged in 2017 murders of Libby German and Abby Williams in Delphi, Indiana

DELPHI, Ind. (CBS) -- More than five years after two teenage girls were killed in Delphi, Indiana, Indiana State Police on Monday announced an arrest in the case.

Richard Allen, 50, of Delphi has been charged with two counts of murder in the deaths of Abigail J. "Abby" Williams, 13, and Liberty Rose Lynn "Libby" German, 14, according to Indiana State Police Supt. Doug Carter. He is being held without bail.

Allen pleaded not guilty his first time ever facing a judge.

"Today is not a day to celebrate, but the arrest of Richard M. Allen, of Delphi, on two counts of murder is sure a major step in leading to a conclusion of this long-term and complex investigation," Carter said. 

Carroll County Prosecutor Nicholas McLeland said Allen is due back in court on Jan. 13 for a pretrial hearing. A preliminary trial date has been set for March 20.

Abby and Libby were best friends in the eighth grade. They disappeared while they were hiking on the Monon High Bridge Trail near Delphi in February 2017. 

Their bodies were found a day later on Valentine's Day in a wooded area, a quarter mile from an abandoned railroad bridge that's part of a trail system where the teens had planned to go hiking during a day off from school.

"Abby and Libby, though in death, have had a profound effect on so many of us; on how we live, and as importantly who we all should be," Carter said, becoming emotional as he spoke.

Police have said Libby snapped a photo of the killer, and recorded his voice on her cell phone before she died. Authorities also have released a series of sketches of the suspect.

In 2017, Indiana State Police first released a sketch of a man they called a prime suspect. 

But then in 2019, without much explanation, the sketch was updated, with a much different-looking man now believed to be the killer. State police did not specify whether Allen is believed to be the man represented in either or both of the sketches, or if someone else may have been involved.

Authorities also did not say whether a man in a screen grab from a video taken by Liberty German is believed to be Allen. The video was taken during what police only called "criminal activity." It is the most important piece of evidence shared with the public to date.

An audio clip from Libby's phone also captured the voice of a man saying, "Down the hill."

Indiana State Police arrested Allen on Friday after searching his home, towing his car, and digging through a backyard firepit.

Allen is a Delphi resident, and lived in the town the whole time the case was under investigation before he was charged. There are fewer than 3,000 people residing in the entire town of Delphi.

We've learned Allen worked at a CVS drugstore on West Main Street.

Photos pulled from social media accounts, since taken down, show Allen and his wife out and about since the 2017 murders. 

Over the years, investigators reviewed thousands of leads, but no arrests were made until now.

Rick Snay told us Monday that he is a friend of Liberty German's family – and spoke about Libby's mom, Carrie's, reaction to the charges.

"This is first time I've ever seen Carrie Timmons smile," Snay said. "I think this is a moment they've been waiting for, for a very long time."

Libby's sister, Kelsi, tweeted on Friday, "Just know how grateful I am for all of you," but no one representing either of the victim's families spoke at the announcement of charges against Allen.

Police and prosecutors declined to elaborate on what led to Allen's arrest, and McLeland said the probable cause affidavit and charging information in the case have been sealed by court order.

"We cannot talk about the evidence that's in the probable cause or the evidence that's in the charging information. That will become evident to you at some point, and it will be released, but right now is not that day," McLeland said. "Today is about Abby and Libby; focusing on them."

"Eventually, you'll be able to see what led us to this day, but again today is not that day," Carter said.

McLeland acknowledged it was unusual to seal the information in a murder case after charges have been filed, but he said it was necessary in this case, because the investigation is still open.

"While all cases are important, the nature of this case has some extra scrutiny with it, and so we – my office, me – felt it was important to seal those records. There will be a public hearing on whether or not those records are going to remain sealed or not," he said. "But for now, to me it's about protecting the integrity of this case. I want to have an opportunity – at some point – to have an opportunity in court to explain the evidence; and for that not to be tarnished, or tainted, or anything like that. Again, he's presumed innocent, and so it was important for me in this case to do that."

The decision not to disclose information left some disappointed.

"The probable cause information – that's supposed to be public knowledge after 24 hours," Snay said. "I understand why they did it, but I'm just frustrated." 

Police received tens of thousands of tips in the case, and have over the years identified several persons of interest, but none ever led to an arrest until now. 

"Since the murders of Abby and Libby 2,086 days ago, the daily investigative team has worked tirelessly," Carter said.

Carter said the case remains an open investigation, even with Allen's arrest.

"We are going to continue a very methodical and committed approach to ensure that if any other person had any involvement in these murders, in any way, that person or persons will be held accountable," Carter said. 

Carter said it was a "very personal moment" for the entire investigative team when they secured Allen's arrest. He said many of them have formed a personal relationship with Libby's and Abby's families that will last a lifetime.

"It was a very, very sad, yet a very humbling experience," Carter said.

Allen's name had not been surfaced from police until his arrest was first reported last week. Our affiliate in Lafayette, Indiana initially confirmed, via anonymous sources, that Allen was arrested and booked on Friday. He is now being held at the White County Jail.

People from the small town of Delphi - about 120 miles from Chicago – were relieved once word spread of an arrest on Friday.

"We're very happy," one woman said. "We're very happy as a community."

"People who knew the girls will never be totally over it, I'm sure," a man said.

"Chills all over my body. Like, I was ecstatic," another woman added. "Finally, some closure for the families."

But Libby German's grandfather, Michael Patty, is not pleased that the suspected killer has been walking free all this time.

"It's always not settled well with me, the fact that that whoever's responsible for this has been walking around now for 5 1/2 years as a free person - and that's not right," said Libby German's grandfather, Michael Patty.

Allen's neighbors told our Indiana affiliate that police were at the suspect's house recently - and focused on an outside burn-pit.

We looked into Allen's background after learning his name and did not find a criminal history. 

Earlier this year, an FBI search warrant obtained by the "Murder Sheet" podcast said the bodies of Abigail and Liberty lost a lot of blood. The warrant also noted that the killer may have staged a murder scene and took souvenirs, but the warrant did not specify what they were.

We connected back on Thursday with Áine Cain and Kevin Greenlee of the "Murder Sheet" podcast to talk about the latest developments on Friday.

"We actually drove up to Delphi, Indiana, in order to try to figure out what's going on," Cain said.

Cain and Greenlee have been digging into the case for their podcast for a long time now.

"This is an incredibly huge and significant development for the Delphi case," said Cain. "Police haven't arrested anyone so far, prior to this."

"The name you mentioned is not a name we heard before today," said Greenlee.

Patty said the same, with some frustration given that Allen lived in town all along.

"You'd asked me two weeks ago – given me that name – it wouldn't have meant anything to me," Patty said.

Patty hopes anyone with information chooses to speak up now.

"There's people out there who probably now can relate – maybe know this guy, and have a bit of information that could help," he said. 

CBS 2's Charlie De Mar asked Patty if he thinks police have the right guy.

"I think not just the police, but prosecutor and judge all signed off on that, so yeah," Patty said.

There will be a public hearing on whether the now-sealed key documents in this case will be made public.  

Anyone with information that could help the ongoing investigation can email abbyandlibbytip@cacoshrf.com, or call (765) 822-3535.