Diamond said no one had been ruled out as a suspect, including members of the girl's family, who continue to cooperate with the investigation.
He said there was no reason for people to panic, but urged them to take the normal precautions of locking doors and windows, and keeping an eye on children when they are outside.
"Right now we don't know if it's an isolated incident or not," Diamond said, adding that there have been no reports of anything similar.
Police presence in the area has been increased as a precaution, he said.
"If, during the course of this investigation, [we determine] an imminent threat to our community, we'll let you know immediately," Diamond said.
Police found Sierra's body on Tuesday about 8 a.m. in a canal about a block from her home. The discovery occurred about 30 minutes after her mother reported the girl missing from the family's home, near 2400 West and 7100 South. There were no obvious signs of a break-in at the home, police said.
At the time the mother called police, her husband had already left for work, Diamond said, but a younger sister and an older brother were home. He didn't know if Sierra might have been specifically targeted.
Sgt. Drew Sanders confirmed Wednesday that surveillance video at the Newbold home captured images, but said he could not discuss what those images showed. With the Newbold family's cooperation, police obtained a search warrant to search their home for evidence. Diamond said Wednesday that police were also following up on some tips.
Sanders said that to preserve the integrity of the investigation, police were withholding information about how long Sierra had been dead before police found her body, the cause of her death, how she might have ended up in the canal and if they recovered DNA evidence.
Diamond said Sierra's family was asking that people respect their privacy during this time.
On Wednesday, Sierra's neighborhood was covered in pink, purple and white ribbons, which had been tied to mailboxes, trees and street signs. Pink and purple were reportedly her favorite colors.
Near her home were two makeshift memorials that included stuffed animals, flowers and a purple butterfly bearing the words: "Fly with the angels, Sierra! We love you."
At nearby West Jordan Elementary School, where Sierra was supposed to start first grade, someone had written "Sierra" on a fence in pink, purple and white ribbons next to a large heart, also fashioned from ribbons.
But the area near Sierra's home remained blocked off by police tape.
A fund has been set up to help pay Sierra's funeral costs. Those wishing to donate can call or visit any America First branch under Sierra Newbold's name.
Police are asking anyone with information about Sierra's death to call them at 801-256-2211.