The name of the person arrested has not been released, but sources say the individual appeared in court Friday morning.
The Indiana State Police Department plans to provide an update on Monday.
Abby, 13, and Libby, 14, were killed in February 2017.
Photos and video taken from Libby's cellphone have given investigators a glimpse into what may have happened in their final moments.
The girls' bodies were found on the property of then-77-year-old Ronald Logan, who is dead. Recent developments indicate Logan asked a relative to lie about his whereabouts on the day of the murders.
Indiana State Police previously said that it was expanding its search for "anthony_shots" profiles, which was used from 2016 to 2017 on social media applications in connection with the murders.
Kegan Kline, a man who police say was using an Instagram and Snapchat account with that username, was arrested in August 2020.
According to a probable cause affidavit, Kline was interviewed by a state police investigator and an FBI special agent after an investigation found he was using an Instagram and Snapchat account with the username "anthony_shots."
Kline is scheduled to appear before a jury in January 2023.
Indiana State Police have interviewed hundreds of people, from possible witnesses and persons of interest to anyone who may have had information about suspicious activity on the day the girls went missing.
More than 50,000 tips have been called in or emailed to investigators during the past five years.
Indiana State Police Superintendent Doug Carter has made it his mission to find the girls' killer. He said this week that he believes authorities will identify the person responsible while he is still superintendent.
Finding the Delphi killer has become an international obsession.
Libby and Abby's story has been told across the country on television and podcasts and debated by people around the world in chat rooms and social media groups online.
This story was originally reported by Lucas Gonzalez on wrtv.com.