He said the FBI was analyzing surveillance video from a home in the area, which may show whether the girl left home on her own or if someone else was involved.
"We're dedicated to trying to get to the bottom of what happened to Sierra," Diamond said during a Wednesday afternoon news conference. "Our hearts go out to the family of this young girl."
Sierra's mother discovered she was gone from her bedroom and called police at 7:27 a.m.
At about 8 a.m., an officer found the girl's body in the approximately four-foot-deep canal, which is across a large field and at least a block from the girl's home.
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.
With the Newbold family's cooperation, police obtained a search warrant to search their home for evidence, Diamond said.
Police taped off the entire block around the house as investigators canvassed area homes and conducted interviews with neighbors. Some officers were seen searching garbage cans for evidence. Diamond said dive teams would be brought to the scene.
Sandra Riesgraf, communications director with the Jordan School District, said Sierra had just completed her kindergarten year at West Jordan Elementary.
Claire Evenson said Tuesday her daughter was best friends with Sierra. The two girls had been in the same kindergarten class together, and were excited to find out they were going to be in the same first grade class together. Evenson described Sierra as a fun girl who loved to play dress up, and tried to include all of the children in neighborhood games. She said Sierra also sang in a church choir with her daughter.
"They liked to make funny faces at each other in church while they were singing," she said. Evensen said police informed her of the girl's death this morning, and she hasn't yet figured out a way to tell her daughter the news.
Katie Dall, 17, works at West Jordan Elementary and said she heard of the girl's disappearance when staff members were asked to keep an eye out for her. She said they searched the school and surrounding areas as a precaution, but never found any sign of her.
Dall said she lives one street over from Sierra's family, and often saw the 6-year-old running around and playing with other kids in the neighborhood.
"The fact that this happened in my neighborhood is very scary to me," she said in an email to The Salt Lake Tribune. "My neighborhood has never had much commotion and I've always thought it to be safe. I know of many children in the area, so I'm sure it's very worrisome to many parents."Cora Jckowski, another neighbor, said she and her husband were doing yard work early Tuesday morning, when Sierra's father approached them, telling them his little girl was missing, and asking if they had seen her. They told him they had seen no signs of her.
Jckowski said the canal where the girl's body was found is visible from their home and that police have been focusing on one specific area of the canal for the most of the day.
The neighborhood was also the scene of a three-alarm fire that destroyed two homes Saturday afternoon. Jckowski said Sierra's death marked the second bad event in their community in a week.
"We've lived here 35 years and this has been our sanctuary," she said. "It's not seeming like it now. The fire was hell enough and now this."
Riesgraf said that while school is no longer in session, counselors will still be called in to help staff members at the school who knew Sierra. She said counseling may also be available to students, if the need arises.
"If we hear there is a need in the community, from friends who attended school, we certainly would see that that need is met as well," she said. "We make sure those services are offered to those who are having a difficult time."