Cops fast-track DNA evidence in eerie teen murder investigation. Picture: Snapchat

The teens, who posted a chilling last Snapchat picture before they disappeared last week, were found dead close to a river near the town of Delphi in Indiana.

Police say they have recovered DNA evidence and have asked the lab to fast-track the vital clue, The Sun has reported.

“We asked for a fast-track as far as that piece of information,” said Carroll County Sheriff Tobe Leazenby.

“So I can’t go into specifics because of the ongoing [investigation].”

Libby German and Abigail Williams' bodies were discovered in the Deer Creek area in Indiana after Libby posted this eerie final Snapchat image. Picture: SnapchatSource:Supplied

It is now the third piece of evidence investigators have said publicly they have, after the grainy suspect photo taken by Libby and chilling audio of a man’s voice saying “down the hill”.

Police haven’t said specifically what kind of evidence they recovered, but DNA forensics expert Dr Gay Bush says that evidence could be anything.

“It can be items found at the crime scene such as a cigarette butt, or a bottle, or a cup or a straw,” Dr Bush told Fox59.

“Or it can be bodily fluids if there’s some kind of assault.”

Mike Patty, Libby’s grandfather, paid tribute to the teen in a heartbreaking video.

He said she loved sport and was a straight-A student.

He told WLFI: “I raised Liberty since she was three years old.

“My wife and I’s relationship with her has been deeply sown with love as we were allowed to play two roles in her life — both parents and grandparents.

“We’re a very tight-knit family with love pouring throughout our lives. Our minds at this stage are stirred in the deepest sorrow you can imagine.

“It is my sincere hope that no one experiences what my family is going through at this time.

“Liberty was taken from us and this will forever be a void in our souls. Yet we find faith in our God.”

Liberty German, 14, and Abigail Williams, 13, were hiking on the historic trail bridge. Picture: FacebookSource:Supplied

Mr Patty also spoke of saxophone playing and her love of music.

He said: “She would often pick at a guitar in her room. What we would give to hear some of those off-key notes today.”

This week investigators released a haunting audio clip of the voice of the prime suspect they believe is connected to the deaths of the two teenage girls.

The recording was taken by Liberty.

Cops believe the voice in the eerie clip taken shortly before the girls were killed could be that of an unidentified man who they’re hunting for.

He was recorded saying “down the hill” which was played several times in a press conference during an update on the double murder investigation that has gripped Delphi, southwest of Indianapolis.

It is unclear whether the man heard in the recording is the same one depicted in an image of a suspect released by authorities last week.

The grainy image released of a man on the bridge at the time of the girls’ disappearance. Picture: Indiana State PoliceSource:Supplied

Police believe that it’s possible more than one person may be involved.

Cops will not say how they got the grainy photo showing a man dressed in jeans and a blue jacket, or why he’s considered a suspect.

The girls were reported missing around 5.30pm on the day of their hike and found dead a day later.

Indiana State Police are looking beyond the town of Delphi for a man photographed near the trail around the time a relative dropped the girls off, Sgt. Kim Riley told WLFI-TV in Lafayette.

Authorities said they are expanding the search for a suspect in the killings of two girls

“We are actually expanding out,” Riley said. “We want people who may have seen somebody walking, that may have picked up a hitchhiker, that may have seen a hitchhiker around that afternoon.”

“During the course of the investigation, preliminary evidence has led investigators to believe the person, in the distributed photo, is suspected of having participated in the murders of Abigail Williams and Liberty German,” said Indiana State Police in a press release.

Police had previously said they considered him a person they wanted to speak with as part of the investigation.

The girls’ bodies were found last Tuesday, one day after they went missing, about a quarter-mile from an abandoned railroad bridge that’s part of a trail system.

The teens had planned to go hiking on the trails during a day off school in Delphi, a community of about 3000 people.

Their deaths have been ruled a double-homicide, but authorities have not disclosed how the girls died. Private funeral services were held Sunday.

A task force made up of FBI agents, state police and local law enforcement is investigating.

This article originally appeared in The Sun and was reproduced here with permission.