TODAY | July 22, 2012
>>> it has been nine days since 8-year-old elizabeth collins and her 10-year-old cousin lyric morris sy went for a bike ride and never returned. a major development in the case. investigators say they have proof the girls are still alive. nbc's craig melvin has the latest.
>> reporter: in a surprising twist, federal investigators now think someone snatched 20-year-old lyric morrissey and 8-year-old elizabeth collins and the little girls are still alive.
>> we feel strongly that the girls are alive.
>> reporter: the fbi spokeswoman says their theory is based on physical evidence. friday, the local sheriff said he believed the young cousins were abducted. while officials are not saying much about their proof, saturday, they made another plea.
>> we feel there is someone out there that has pertinent information about the girls' whereabouts and we would like to take this opportunity to ask them to come forward.
>> reporter: federal officials revealed they're interviewing persons of interest, but said they would like more help from those closest to the girls.
>> law enforcement has not received total cooperation from all family and close friends.
>> reporter: lyric's parents have not been named suspects or persons of interest, but court documents show extensive criminal records including convictions involving drugs. lyric's mother, misty, told our affiliate in iowa, she and her husband hired an attorney after police awakened them in the middle of the night .
>> we were put into rooms and we were for three hours accused of taking our children, told that we did it, that we need to tell them where the children are at.
>> reporter: the parents of both girls deny any involvement.
>> we just want our babies back.
>> reporter: the cousins vanished friday, july 13th , after riding their bikes near meyers lake . their bikes and a purse were found nearby along a nature trail , but there were no signs of a struggle or their shoes. the 25 acre lake was dredged, drained and the fbi dive team called in. worried neighbors went door to door , some scoured nearby woods. now, those neighbors wait and hope for a happy homecoming. for "today," craig melvin, nbc news, new york.