Authorities believe that the kidnapped girls from Iowa are still alive. The girls bicycles were found in Evansdale (a small town northeas of Iowa) as Meyers Lake. FBI publicly declared they will interview everyone that was there at the time.
FBI did not release a strong argument to support their theory and although FBI might have such an argument they want to keep it secret until the investigation is over.
Although several suspects and believed witnesses were interviewed up until this date, authorities still rely a lot on tips received from local people in order to cover more theories. The case is far from over.