DELPHI, Ind. (AP) — An FBI effort using electronic billboards to seek information in the killings of two Indiana teenagers is expanding to dozens of states.

State Police Sgt. Tony Slocum said Friday the billboard push that began across Indiana will expand soon to 45 other states to solicit tips in the killings of 14-year-old Liberty German and 13-year-old Abigail Williams.

He says the privately-owned billboards will display photos of the girls, an image of a man considered the main suspect and a telephone tip line. Those calls are being funneled to the FBI’s Major Case Contact Center in Washington D.C.

The Delphi girls’ bodies were found Feb. 14 in a rugged area near a hiking trail in the small city about 60 miles northwest of Indianapolis, a day after they vanished while hiking during a day off from school.

Police said Thursday they’ve received about 3,900 tips in the killings. About half of those tips were received after authorities released an audio clip Wednesday taken from a video German had recorded on her cellphone.

Investigators said that audio captured a man saying “down the hill” and they believe he participated in the killings. Authorities said they aren’t certain if the voice is that of a man shown in a blurry image also taken from a video on German’s cellphone.

Authorities have called that unidentified man the main suspect in the murders.

State Police Sgt. Tony Slocum said Thursday there have been no arrests in the killings and no one is in custody. He urged residents not “jump to conclusions” if they happen to see law enforcement activity.

State Police say the reward for information leading to an arrest or arrests in the case has grown to $50,000.

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