EVANSDALE, Iowa (AP) - Law enforcement officials will likely expand their search for two missing Iowa cousins now that the girls' disappearance is considered an abduction case, experts said.

But experts said it's hard to tell exactly what's going on because officials probably aren't disclosing everything they know, including why they are confident that 10-year-old Lyric Cook-Morrissey and 8-year-old Elizabeth Collins 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. July 13. That's where the girls' bicycles were found.

Breault's plea for help fits with what David Finkelhor, director of the Crimes Against Children Research Center, expected would happen after the case was reclassified as an abduction. He said investigators now 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, who is based at the University of New Hampshire.

Finkelhor said if the girls were abducted by a stranger, the statistics are grim — his research shows that 40-50 percent of children in that situation aren't recovered alive. But, he said, abductions by strangers are so rare that it's difficult to predict what might happen.

Several "persons of interest" have been interviewed in the case, and numerous tips from the public have come into investigators. Breault also said that 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 no longer cooperating with police. He has been placed in a pretrial supervision program in two separate drug cases, so parole officers are monitoring Morrissey's 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.

Investigators spent much of last week searching Meyers Lake and the surrounding area, which is about 120 miles northeast of Des Moines. 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.

Breault said investigators believe even the smallest details could be crucial in this case, so she encouraged anyone who had been at the lake, located near Interstate 380, to call — even if they didn't see the girls.

"Don't assume we know what you know," she said.

Breault said no arrests had been made as of Sunday, but she declined to comment on details of the investigation.

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.

The group has been helping with the search for the Iowa cousins, so he couldn't comment directly on details of the case. But he said the fact that investigators actually drained most of Meyers Lake shows how serious they are about investigating every lead.

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."

Smart was kidnapped at knifepoint in 2002 in Utah by a handyman who knew her family. Motorists spotted her as she walked with her captors nine months later.

Dugard was taken off a South Lake Tahoe, Calif., street in June 1991 while walking to a school bus stop and was held captive in a backyard compound for 18 years. She was discovered in August 2009 when authorities said her captor took her and her children to a meeting with his parole officer.