For the safety of students, Calaveras County deputies patrolled Jenny Lind Elementary School in Valley Springs, as classmates of victim Leila Fowler were greeted by instructors as they somberly returned to school.
Grief counselors were also expected to be available at the school, where a class of sixth-graders placed ribbons outside to remember Fowler, a third-grader.
"It's scary," student Marilou Sandoval told KOVR-TV. "You never know what kind of people are out there."
Authorities said Leila was fatally stabbed on Saturday at her home in Valley Springs during an apparent break-in. The girl was found by her 12-year-old brother who told deputies that he had encountered a male intruder in the home.
On Sunday, door-to-door sweeps proved fruitless as authorities urged residents to lock their doors and watch streets and yards for the suspect, whose description was vague.
"A lot of us here are used to keeping our doors unlocked, our cars unlocked and I'm sure a lot of families last night locked all of their windows, locked all of their doors for the first time," Connie Brodie, who lives in nearby Rancho Calaveras told KOVR on Sunday.
The manhunt has been joined by the sheriff's departments of Calaveras and surrounding counties, California Highway Patrol and state Department of Justice. Sheriff's officials say investigators collected fingerprints and what they believe is DNA from the home.
"This is way too close to home," Julia Poland, who took her 13-year-old daughter to a news conference on the search, told the Modesto Bee. "This kind of thing does not happen here."
Calaveras County sheriff's Capt. Jim Macedo told reporters the brother is currently not considered a suspect and has been cooperating with investigators.
Authorities spent the weekend conducting a door-to-door sweep of homes scattered across hilly terrain, checking storage sheds and horse stables, and even searching attics.
"It is a difficult area to search, it's rural, remote," Macedo said.
Investigators on Sunday were interviewing several people, but no suspects had been named.
Investigators were asking area residents to call authorities if they had any information, knew of anyone who had unexplained injuries, or may have left the area unexpectedly after the girl was killed.
Valley Springs is a community of about 2,500 people in an unincorporated area of Calaveras County, known as "Gold Country," in the foothills of the Sierra Nevada mountains, about 60 miles southeast of Sacramento.
Copyright 2013 The Associated Press.