updated 10/19/2011 AT 7:00 AM ET
•originally published 10/19/2011 AT 8:00 AM ET
When Jeremy Irwin returned home from work in the early morning hours of Oct. 4, he found his fiancée, Debbie Bradley, and two sons asleep.
But when he peeked in on then 10-month-old daughter Lisa, her light was on and the crib was empty.
That, Irwin tells PEOPLE in this week’s cover story, “is when all hell broke loose.”
Since little Lisa’s strange disappearance two weeks ago, investigators have been struggling to determine exactly what happened to the bubbly girl whose family called her “Pumpkin Pie.”
The spotlight has fallen on Irwin, 29, and Bradley, 25, who says she volunteered to take a lie detector test but that when she took it she was “terrified and nervous and worried about my daughter. They told me I failed.”
“We have absolutely nothing to hide,” says Bradley. “Let them search all they want, but do not take the focus off finding my daughter.”
For much more on the Baby Lisa story, pick up this week’s issue of PEOPLE, on newsstands Friday