EVANSDALE, Iowa, July 21, 2012 -- The FBI said they have evidence that leads them to believe that two missing Iowa girls are still alive.
"We believe the two girls are alive," FBI spokeswoman Sandy Breault told ABC News. Breault said this belief was based partly on the evidence found Friday, but would not elaborate further.
Authorities reclassified the case as an abuduction on Friday.
Elizabeth Collins and Lyric Cook, who are cousins, were last seen on July 13, riding their bikes near a lake in Evansdale, Iowa. A $50,000 reward is now being offered for information that would lead to their being found.
Elizabeth Collins' mother said she was overjoyed to hear the FBI say they believe the two girls are alive.
"That is amazing," Heather Collins said. "That is the best news we have heard all week...keep praying we will have them back..."
An FBI dive squad with sonar equipment Friday searched Meyers Lake, near where the girls' bikes were found on a nature trail. Officials said that they only continued to search the lake to be "100 percent" certain the girls were not in it. The girls' families have been adamant that they believe the girls are somewhere else.
"The girls aren't in the lake. We've all been convinced of that basically since Friday [July 13]," Craig Ceilley, a family spokesman, told ABC News Friday. Lyric Cook is 10; Elizabeth Collins is 8.
As the mystery grows about the cousins' disappearance, so does the list of questions surrounding Lyric's parents, Misty and Dan Morrissey. Both have been convicted of felony drug offenses and spent time behind bars. Misty served four years in federal prison.
Even their relatives acknowledge that the couple's troubled past could have played a role in the girls' disappearance.
"I can't rule that out, you know," Tammy Brousseau, the girls' aunt, told ABC News Thursday. "I want every stone unturned."
In the past week investigators have questioned both Misty and Dan Morrisey several times. Brousseau said Dan Morrisey at one point left a police interview because he felt he was being treated like a suspect.
"I can see Dan becoming very defensive after he's being told, you know, 'You killed your daughter and niece. You know you did. We have proof. We have evidence that you did this,'" Brousseau said.
Brousseau said the Morrisseys, who are separated, have a violent past that even involves a restraining order.
"At one point Dan had assaulted Misty and that's where the no-contact order came into place," she said.
On Wednesday night investigators went to a nearby hotel where Misty and Dan Morrisey were staying, but Dan claimed he was tired and wanted to go to sleep. The following morning Misty took a urine analysis and a polygraph test. However, Brousseau said the pair had been advised by their attorney not to speak any further to police or the media or submit to any more polygraph tests.
Capt. Rick Abben, the spokesman for the Black Hawk County Sheriff's Office, said Thursday that their silence was not helpful to investigators.
"It's a distraction for us, and why they wish to do that, I don't know," Abben told reporters. "We're asking for 100 percent cooperation. Why they don't want to do that, I have no idea."
Late Thursday Misty and Dan Morrisey were spotted leaving the authorities' makeshift command center in Evansdale, with Misty in tears.
"They have no idea about anything," Misty yelled as she left the building.
"Back off," said Dan as reporters gathered around them.
With the search for the girls now more than a week old, family members want the focus to be on the two cousins, not Lyric's parents.
"Let's focus on Elizabeth and Lyric. Let's leave the past where it belongs," Ceilley urged Friday.
If one family member is getting roughed up, he said, "they're all getting roughed up."
ABC News' Olivia Katrandjian contributed to this report.