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.”