“The Delphi Murders: Who Killed Abby & Libby?” premieres tonight at 10 ET on HLN.

Delphi, Indiana CNN  — 

A five-and-a-half-year nationwide search for a suspect in the killings of two Indiana teens ended with the arrest of a local man, authorities said Monday.

How investigators came to arrest 50-year-old Richard M. Allen, of Delphi, will remain a mystery for now, as a court has sealed charging documents and the investigation remains open, but authorities say Allen is charged with two counts of murder in the 2017 slayings of Abigail Williams, 13, and Liberty German, 14.

The pair went for a hike along Delphi Historic Trails in February of that year but never showed up at a previously arranged time to meet Libby’s dad, police said. Their bodies were found the next day in a wooded area near the trail, about a half mile from the Monon High Bridge where they’d been dropped off, according to police. A grainy video of a man walking and a garbled voice recording were among the scant clues authorities publicized over the years.

Neighbors saw police searching Allen’s home two and a half weeks ago, they say. Police arrested Allen on Wednesday, according to a news release, and formally charged him Friday before transporting him to White County Jail. Allen is being held without bail.

“Today is not a day to celebrate, but the arrest … is sure a major step in leading to a conclusion of this long term and complex investigation,” Indiana State Police Superintendent Doug Carter told reporters.

Asked the family’s reaction to news of Allen’s arrest, Carter said, “It was a very sad, yet a very humbling experience.”

Allen pleaded not guilty at an initial hearing, Carroll County Prosecutor Nick McLeland said. He is scheduled to return to court for a pretrial hearing January 13. His trial is slated to begin the morning of March 20, the prosecutor said.

Suspect assisted with funeral photos, aunt says

CVS confirmed that Allen worked for the drug store chain but did not specify where. The company is shocked and devastated, it said in a statement, and stands “ready to cooperate with the police investigation in any way we can.”

Libby’s grandmother, Becky Patty, and aunt, Tara German, were informed someone was in custody Wednesday, and on Friday, they learned it was Allen, who police said worked at the CVS in Delphi, they said. Patty does not know Allen, she said, but German is a regular at the CVS and knew Allen from shopping at the store. She recalled a specific encounter with Allen following Libby’s death.

“I went into the store to print photos of Libby for the funeral, and he was the one who helped me,” German said. “I was a mess trying to get the images off my phone. Once they were printed, he looked at me and said, ‘I’m not gonna charge you for this.’”

While McLeland said a judge had found probable cause to charge Allen with murder, he declined to elaborate on the reasoning, saying the charging documents and probable cause affidavit were sealed. A court will revisit the decision to seal the documents later, he said.

In the meantime, tip lines remain open, he said, and investigators are seeking information “not only about Richard Allen, but about any other person you may have.” McLeland declined to elaborate on whether authorities are seeking additional suspects.

Liberty German, left, and Abigail Williams were killed in 2017.

“I know it’s frustrating,” he said. “My goal is to maintain the integrity of this case.”

Following Monday’s news conference, Carter told HLN he had “already gotten tips directly since 10 o’clock.”

Carter also declined to provide many details, saying, “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 person will be held accountable.”

“This investigation is far from complete,” he added, “and we will not jeopardize its integrity by releasing or discussing documents or information before the appropriate time.”

While details are not yet forthco