(CBS/AP) EVANSDALE, Iowa - Law enforcement officials will likely expand their search for missing Iowa cousins Lyric Cook-Morrissey and Elizabeth Collins now that it is considered an abduction case, according to experts.
Officials aren't disclosing why they say they are now confident that Elizabeth, 8, and her 10-year-old cousin Lyric are alive.
FBI spokeswoman Sandy Breault said Sunday that investigators want to talk to anyone who was at Meyers Lake in the northeast Iowa town of Evansdale before 3 p.m. on July 13. The girls' bicycles were found in that area.
Director David Finkelhor of the Crimes Against Children Research Center said now that the case has been reclassified as an abduction, investigators may be more dependent on tips from the public.
"They've got to cast a much wider net. They could be miles from that spot there," said Finkelhor.
Breault said several "persons of interest" have been interviewed in the case, and numerous tips from the public have come in to investigators. Most of the girls' family members have been cooperating with investigators.
Lyric's father, Daniel Morrissey, is being watched closely by authorities but has not been named a suspect. Morrissey, 36, has a lengthy criminal history and is in a pretrial supervision program in two separate drug cases, so parole officers are monitoring his actions.
Misty Cook-Morrissey, 34, also has a criminal record. She was convicted of federal drug charges and state theft and alcohol violations. She is currently on supervised release. She took a second polygraph test on Monday.
Investigators spent much of last week searching Meyers Lake and the surrounding area. The lake was mostly drained and the FBI used sonar technology and divers to search it, so investigators could ensure that the girls were not there.
A director at the National Center for Missing and Exploited Children said it is incorrect to assume that the lake search was the focus of the investigation just because it was the most visible.
"There were a lot of other things, I assure you, going on simultaneous to that lake, but law enforcement was right to eliminate that as a possibility," said Robert Lowery, the executive director of the group's missing children's division.
Breault said no arrests had been made as of Sunday, but she declined to comment on details of the investigation.
Lowery said there's reason to be optimistic, pointing to cases where missing children were found long after they disappeared, such as Elizabeth Smart and Jaycee Dugard.
"We can't lose hope," Lowery said. "There have been many instances where children have been gone hours, days, weeks, months and even years. And we found the children and returned them to their families."