The sheriff in charge of the double murder investigation of two teens in Indiana has told DailyMail.com that despite 11,000 tips from across the U.S., a sweep of the county's sex offenders' register, a $219,000 reward and 200 investigators working daily on the case, they are no closer to solving the crime.

Liberty German, 14, and Abigail Williams, 13, were found dead on February 14 close to Deer Creek along Delphi Historic Trail near the town of Delphi.

Three weeks on, police have made no arrests and have not located the prime suspect.

Two weeks ago, police confirmed that a man walking along Monon High Bridge near the trail, around the same time as the girls, was who they were looking for.

Abigail Joyce Williams, 13 (left), and Liberty Rose Lynn German, 14 (right), were found dead on February 14 this year

The Sheriff in charge of the investigation, Tobe Leazenby, tells DailyMail.com that police have made no progress towards the murder - or murderers despite receiving over 11,000 tips

Investigators revealed that a grainy image of the suspect had been captured by Liberty on her phone and that she had also managed to record audio of a voice saying, 'Down the hill'.

Carroll County Sheriff Tobe Leazenby told DailyMail.com that not a single tip was being discounted, for fear it could be the one that cracked the case. Tips have come from the local area, throughout the Midwest and as far as Los Angeles.

'We have no one jailed at this point so everything helps,' he said.

'I've received tips like, 'I was at Walmart parking lot and I saw this guy wandering around and he looked really similar to the guy in the photograph' or 'I was behind a guy at a supermarket and I heard him speak and something in my mind said that was him.'

'Some are quite adamant, I understand that, I accept that. That's partly why this is taking so long because we have got to look into it. In the back of our minds that tip may be 'the one'.

Known sex offenders in Carroll County had been ruled out, Leazenby said.

Police are still appealing for information after failing to produce a strong lead. The main suspect is pictured on the above flyer (left) and in grainy footage captured by one of the victims on Snapchat (right)

The Carroll County Sheriff's Office, above, is the lead agency on the case. Leazenby said that not a single tip was being discounted and that tips have come from the local area, throughout the Midwest and as far as Los Angeles

Leazenby also said that every sex offender in Carroll County has been questioned and sex offenders across Indiana have been investigated. Above, a wall designated as a tribute to Liberty and Abigail at the command center for the investigation in Delphi

Along with following up on tips, investigators are continuing to canvass areas of Carroll County. 'As far as search warrants, we've had a couple that did not come to fruition as it relates to completion of the case,' the sheriff said

'That was one of the things we first got into, the sex offender registry. We went through the whole list locally then we enlarged that statewide and checked practically every individual.

'We asked each sheriff of the other 91 counties in the state to look into certain individuals that had questionable alibis or schedules. That was done really early. That road has been traveled.'

Along with following up on tips, investigators are continuing to canvass areas of Carroll County.

'As far as search warrants, we've had a couple that did not come to fruition as it relates to completion of the case,' the sheriff said.

He would not elaborate on why the search warrants had been served or who they had been served upon.

Carroll County Sheriff's Office is the lead agency on the case. They have been assisted by the Department of Homeland Security, the FBI, Indiana State Police, Delphi Police Department and detectives from sheriff's offices and police agencies across Indiana.

'Some of the detectives have been here since day one,' Leazenby said. 'A few of them have forensic skills or are polygraph operators.

'There have been individuals that we've asked to take polygraph tests. That's an additional tool we use to eliminate an individual from the process if need be, to clarify what they are telling us is actually the truth.'

A small memorial has been set up at the foot of Monon High Bridge, near where the bodies of Liberty and Abigail were found

People left flowers on the grass by the side of the road as a tribute to the girls

Tie-dyed ribbons can also be seen around trees and poles throughout Delphi, in honor of of Liberty German's love of tie-dye

The sheriff said anyone who was asked to take a voluntary polygraph test had complied and had passed.

Several agencies have become involved from Illinois and Ohio. 'They are following up on tips there and the investigation has spread into neighboring states,' Leazenby said.

He said that the involvement of the Department of Homeland Security was for 'mainly equipment and logistics, even notepads, providing us with office supplies'.

The sheriff shared details on how the large investigation was being conducted, beginning every morning with a cross-agency briefing and prayers.

'We gather at the command center for daily prayers before starting our meeting. Then we have a daily update from those in charge. They go through developments from the previous day or days. When the meeting is over, investigators are assigned the leads that are still coming in from the phones and emails. Investigators are usually paired up, go out into the field and follow up on those tips.'

The sheriff said there could 'possibly' be more than one suspect but would not speculate if the murders were connected to any larger operation.

'To me, it doesn't make any difference what the number [of suspects] is as long as we get those responsible behind bars.'

He said that he was unaware of any cases which appeared to be connected to the Delphi homicide investigation.

'We have had instances of individuals who have violated probation with drug possession or something along that line. Minor new cases have developed but nothing associated with these homicides.'

That includes claims of a link to the murders of cousins Lyric Cook and Elizabeth Collins, who were kidnapped as they rode their bikes at Lake Meyer near their grandmother's home in Evansdale, Indiana in July 2012.

Their murders have never been solved and claims surfaced Wednesday that police were looking at for a link but none has been found.

So far, the best evidence in the case has come from the girls themselves - and may be the key to solving the crime.

Leazenby said that after the release of the photograph and audio recording, their tip line was flooded with calls.

Liberty posted what are likely to have been the girls' final moments alive on Snapchat, sharing photographs of their hike along Delphi Historical Trail (above)

The bridge (above after their murder) was the last place the pair were seen alive

Police found the girls' bodies on a property nearby the following day. They searched it and a car on it (above) afterwards but none of those who live there are suspected of killing the pair

'This was before the FBI took over the tip line. We forewarned our folks that were locally manning the tip line, 'Hold on, here it comes' - and it did. I'm not complaining when I say that because we need those tips.'

The victims' families had been informed of what the girls had recorded before it was made public.

'I think it's offered some healing through their grieving process,' the sheriff said. 'When they knew that she had captured that, they were - proud is the word I'll use. 'She had the mindset to go, 'Something doesn't feel right here, so I'll push the record button.'

He added: 'For her to do what she did in collecting that - I'm not sure where we would be right now with the investigation without that.

'In essence that little girl may, in a roundabout way, end up solving her own crime.'

Leazenby would not comment on whether the girls had recorded anything else, citing the need to protect the evidentiary process.

The family of Liberty German will hold a press conference on Thursday in the Carroll County Courthouse to increase awareness of the investigation. The family of Abigail Williams have decided not to take part at this time.

Liberty's grandfather, Dennis Bridge, told DailyMail.com last month that his 'strong-willed girl, she put up a fight'.

He added: 'Beautiful girl, I'm going to miss her. She's supposed to come to my funeral not me go to hers.'

A memorial of flowers, angel ornaments and a glittery bunny rabbit for each girl now sits close to the bridge where they were last seen alive. Ribbons made of tie-dye fabric, which Liberty loved to wear, flutter in the nearby trees.

The town of Delphi is dotted with pink and purple ribbons in remembrance of the girls and in shop windows, posters remind people of the tip line number. The reward to find the killer is now $219,000 and fundraising continues.

The sheriff, who has spent 30 years in law enforcement, said this case was 'not like anything I've ever had in my career'.

'It's trying but I'm a man of faith, that's where my hope and prayer comes from. That keeps us driving forward,' he said.

'I'm very impressed with the team that we've got on board all the way from local to federal.'

Liberty and Abigail were laid to rest at separate funerals in Delphi last month. Hundreds lined the town's streets to pay their respects

At a press conference to launch the homicide investigation three weeks ago, the sheriff said he did not believe there was a threat to the local community. He told DailyMail.com on Tuesday that he wanted the public to remain on high alert for anything out of the ordinary.

'Now more than ever it's vitally important to be vigilant, mindful and watchful. From a personal standpoint, hold your children even closer,' he said.

'Any one of us, including me, take so many things for granted. Do I feel there is a threat that still exists here? There's always the possibility that some kind of evil will rise no matter where it is.

'I want folks to be additionally cautious in their approach with life.

'I've preached this ever since I became sheriff - if you see something that just doesn't look right, get a report in. We can't see everything and having that additional set of eyes and ears is of big importance to us.

'Thank you for anyone who has played a role whether it's a phone call or a message.'

Leazenby also spoke directly to the killer who remains at large.

'As I've said since day one, I feel this within the deepest part of my soul as sheriff, that we will resolve this.

'To anyone that may know of this individual and is wanting to provide information - I come from the old school that good does win over evil. The person involved will be found and will be prosecuted.'

Anyone with information can call Delphi Homicide Investigation Tip Line at 844-459-5786 or 1-800-225-5324. Tips can also be emailed to abbyandlibbytip@cacoshrf.com. Information can be reported anonymously.