DELPHI, Ind. -- State police were planning to release a composite sketch Monday of the main suspect in the killings of two teenage girls who disappeared from a hiking trail near their hometown in northern Indiana in February.

The sketch is "an artist's composite of the information" collected by all the agencies involved in the double-murder investigation, including the FBI, said Indiana State Police Sgt. Kim Riley. Riley said investigators consider the sketch a "very important" development in the ongoing investigation.

"It will give people a clearer image of who we are looking for," Riley said.

Fourteen-year-old Liberty German vanished with 13-year-old Abigail Williams on Feb. 13 while hiking near Delphi, about 60 miles (100 kilometres) northwest of Indianapolis. Their bodies were found the next day in nearby woods. No arrests have been made in the slayings and authorities have not disclosed how the girls were killed.

Investigators released two grainy images in late February of a man they consider the main suspect in the killings. They also released audio of a male saying "down the hill."

That evidence came from German's cellphone. Riley said investigators believe the man captured in the photos killed both girls.

The police tip line for the case is 844-459-5786. Tips can also be reported by emailing Abbyandlibbytip@cacoshrf.com.