An extensive search involving local, state and federal investigators has failed to find them. FBI spokeswoman Sandy Breault said there was "nothing new" about the case Tuesday.
Breault stood by her assertion, first made Saturday, that investigators believe the girls are alive.
"They are not going to reveal the reasons why. You wouldn't want them to do that. It would jeopardize the investigation and the children," she said.
David Finkelhor, director of the Crimes Against Children Research Center at the University of New Hampshire, said that claim means investigators could "have something quite important" for evidence. He said cases of two children being abducted by a stranger were rare since it would be hard for one person to control both, which makes the common motive of sexual gratification less likely in this case.
He said it makes sense to look into whether the abduction is linked to pending drug charges against Daniel Morrissey, Lyric's father, a habitual felon facing decades in prison on charges of conspiracy to manufacture methamphetamines. In other cases, children have been kidnapped by rivals out of retaliation or held hostage to prevent incriminating testimony, he said.
"If they do think the dynamics are primarily around the drug cases, investigators might be more likely to think the girls are alive. They lose their value if they have been murdered," he said.
Court records show Morrissey, 36, appeared in court for a change of plea hearing in one of his drug cases the day before the kids vanished but did not plead guilty. Prosecutor Brad Walz said such hearings usually indicate a guilty plea is forthcoming, but declined comment on why Morrissey did not enter one.
David Mullin, a defense attorney for Jason Stolfus, who was arrested with Morrissey and faces the same charges, said the prosecutor told him Morrissey's plea agreement "fell through." He said police reports show Morrissey implicated his client in crimes after both were arrested in December. But he said Stolfus would not have a motive to take the children because he has been offered a favorable plea deal in which he would likely avoid prison.
"The consequences will be so little that it would hardly be a motive to witness tamper or anything like that," Mullin said. The charges against Morrissey, on the other hand, carry 45 years in prison apiece because he is a repeat offender.
Cook, the girls' grandmother, said she doubted the abduction was linked to drugs but could not rule it out. She said Dan Morrissey voluntarily turned his cellphone over to investigators in recent days and explained all the calls he made and received.
"I mean there could be a side chance of somebody that hates him or something, I don't know," she said. "Everybody is being checked out."
Cook said she is "praying so hard" for the girls' safety while picking over the details of the day she last saw them, when they left for a bike ride at 11:30 a.m.
Cook said Lyric knew she had to return home shortly because Lyric and Cook planned to leave for the home they shared in nearby Waterloo with Lyric's mother, Misty Morrissey, by 1:30 p.m. Cook said she expected the girls to return for lunch or a drink of water or juice as they always did when they were playing in the heat.
"That's what's just so strange about all of it," she said.
Cook said she got nervous when they weren't back by 12:30 p.m. and started driving around town looking for them. After an hour of searching, she returned to the home. Cook said that Misty Morrissey stopped by after getting off work.
"Misty said, 'Mom, you go home and I'll just wait for Lyric and bring her home," Cook recalled.
Cook said she drove to her home but was soon told by Elizabeth's father the girls hadn't surfaced. A firefighter found the bikes two hours later, and the manhunt began.