DELPHI, Ind — Libby, 14, and her best friend Abby Williams 13, were walking along a hiking trail in rural Delphi when their throats were cut and they were left in the woods on Feb. 13, 2017. Their bodies were found the next day.
Allen was arrested in 2022 and has pleaded not guilty to murder.
ABC News' Janel Klein contributed to this report.