DELPHI, Ind. -- Finding Abby and Libby’s killer remains a top priority as the investigation enters its second year and detectives are using every resource available to help them solve the crime, that includes asking outside law enforcement agencies to review their case.

Call 6 Investigates has learned that Delphi investigators have asked the Georgia Bureau of Investigations and agents from other FBI field offices to look over the case with a fresh set of eyes in and offer recommendations in the hopes of finding the missing puzzle piece that will help them solve the crimes.

Those recommendations and conclusions are not being released to the public, but the expertise of outside departments is meant to assist in making sure that no stone is left unturned in the search for Libby and Abby's killer.

Indiana State Police say they have worked with a number of agencies across the country as they track down leads from the thousands of tips they have received.

In response to a request from Call 6 Investigates' Paris Lewbel, Indiana State Police say it is common for investigators to seek reviews from outside agencies for complex investigations like Delphi.

"Thank you for your continued interest in the Delphi homicide investigation. While I'm not able to speak directly to your questions, I can share with you that it is common with complex investigations to share information with other police agencies, inclusive of the FBI, who, as you know, has been part of this investigation. Information shared between agencies does become part of the investigation, and, as you know, the state police does not speak to specifics of an active investigation, inclusive of speaking to investigative methods.

The prime suspect in the case remains an unnamed man behind a witness sketch, two photos and a voice clip that were captured on Libby’s cell phone the day the girls were killed.

Investigators have cast a big net in their search for the killer with more than 30,000 tips coming in from around the country.

But in the year since Abby and Libby were murdered, no arrests have been made.

State police ask anyone who recognizes the above images or voice or has any other information about the case to call the Tip Line at 844-459-5786 or 1-800-225-5324 (800-Call FBI). Tips can also be emailed to AbbyandLibbyTip@cacoshrf.com

MORE DELPHI | One Year Later: Who murdered Libby & Abby