However, police in the nearby suburb of Arvada said they were investigating whether the disappearance of Jessica was related to two recent child enticement cases that involved a man who tried to lure two boys about the same age as Jessica into a car.
No suspects were identified in those incidents, which took place about 6 miles south of Jessica's home.
"There's no connecting factor right now," said Arvada police spokeswoman Jill McGranahan.
A resident in a neighborhood in Superior, a town along U.S. Highway 36 linking Boulder and Denver, reported finding the backpack on a sidewalk.
Police declined comment about its contents. Materasso said it was sent to the state crime lab for analysis that involved DNA samples from the family.
Authorities got a late start searching for Jessica because her mother works nights and slept through a call Friday from school officials after Jessica didn't arrive for classes.
People in the area have been moved to help in the search.
More than 800 volunteers turned out for Saturday's search, and at least 300 leads have been called in to a tip line.
So many police fliers have been posted on fences and windshields around the city that authorities were having trouble keeping up with demand for the material.
Banda reported from Denver.