DELPHI, Ind. (NewsNation Now) — Four years after two teenage girls were killed in northern Indiana during a winter hiking trip, authorities say they are still “diligently” investigating the unsolved slayings and seeking more tips.

Indiana State Police said in a statement that the state agency and other law enforcement departments “continue to actively investigate all tips and leads we receive” in the 2017 killings of Liberty German, 14, and Abigail Williams, 13.

Their bodies were found in a rugged area near a hiking trail on Feb. 14, 2017, one day after they vanished while walking on that trail near the Monon High Bridge, just outside their hometown of Delphi, about 60 miles northwest of Indianapolis.

The state police statement said investigators “continue to work diligently to bring this case to a close,” and adds that, “this type of violent crime cannot and will not go unanswered.”

Within days of the killings, investigators released two grainy photos of a suspect walking on the abandoned railroad bridge the girls had visited, and an audio recording of a man believed to be the suspect saying “down the hill.”

Authorities have since released two sketches of the suspected killer, including one in April 2019 based on video from German’s cellphone that’s believed to be more accurate than a sketch released in July 2017.

Police also released video in April 2019 which shows the man suspected of killing the teens walking on the abandoned railroad bridge the girls had visited.