(CBS/AP) IOWA CITY, Iowa - Misty Cook-Morrissey, the mom of one of two missing Iowa cousins agreed to submit to a second polygraph test Monday to show she is again cooperating with investigators searching for the girls, their aunt said.
Cook-Morrissey was going through the so-called lie-detector test Monday with state and federal detectives at an elementary school in Evansdale, her sister, Tammy Brousseau said. Misty is the mother of 10-year-old Lyric, who vanished with her 8-year-old cousin Elizabeth on July 13 while riding bikes near a lake in the northeastern Iowa town.
Brousseau said Cook-Morrissey submitted to one polygraph last week, but the mother announced she would not take any more after claiming she was harshly interrogated and accused of involvement in the disappearance. Investigators reportedly called the lack of cooperation a distraction for their search.
"Because Misty did not want to do the second polygraph test at the advice of her attorney, because she didn't want to be coerced and cornered and told that she did this, there was a little bit of separation," Brousseau said. "Some of the family members felt, `OK, she's not cooperating 100 percent.' I hope that turns around now."
Cook-Morrissey is cooperating again now so she can put to rest the idea that there is a family member not cooperating, Brousseau said.
The girls' bikes were found near Meyers Lake which launched a search involving hundreds of local residents who failed to find the girls. An FBI dive team using sonar equipment concluded last week the girls were not in the lake.
Investigators said over the weekend they have reason to believe the girls are alive, and they are treating the case as abduction.
Black Hawk County Sheriff's Capt. Rick Abben said last week that investigators were examining "every aspect" of the criminal histories of Cook-Morrissey and her estranged husband, Dan Morrissey, so that they do not overlook any possible leads. He said they were not suspects in the disappearance.
Brousseau said Morrissey also went through a second polygraph test over the weekend after initially declining to do so. Brousseau said the couple had been advised earlier to stop cooperating with police after consulting with Waterloo attorney Tom Frerichs. However, Frerichs said Monday he was not representing the couple.
Cook-Morrissey agreed to Monday's test on the condition that a family member -- she picked Morrissey -- be present in the room, Brousseau said. The FBI also promised that she would not face any accusatory interrogation.