Relatives had called police to report they had not heard from the woman a retired elementary school teacher who lives alone since Saturday.
Her body was found inside the house, and officers immediately believed the death was suspicious.
An autopsy initially concluded the victim was an adult woman and was suffocated, UPD Lt. Justin Hoyal wrote in a Thursday news release.
"It is not known at this time what was used to kill the victim," Hoyal wrote.
Hoyal had earlier declined to say whether the victim was the missing homeowner or identify her in any way, pending family notifications.
Also, before the autopsy, investigators were unable to identify the body as male or female, but Hoyal would not discuss the reason for that, claiming those details could jeopardize the investigation. He added that the body was not mutilated or dismembered.
Police also declined to say where in the house the body was found; there were no indications of a forced entry, UPD acknowledged.
Investigators have no leads as to a suspect, Hoyal wrote. Anyone with any information about the crime or who saw anyone suspicious in the area of the house since Saturday is asked to call UPD at 385-468-9816.
Neighbors described Steffey as a nice woman who liked children. They called her the "sun tea lady" because she put out jars of the beverage every morning.
"She would always have one or two of them," neighbor Laura Zamudio said.
Steffey often would invite neighborhood children, including Zamudio's, to play and provided chalk so they could draw on the sidewalk, Zamudio said. She last saw Steffey on Friday being dropped off at her home after she apparently had been grocery shopping.
"She was a very nice lady," Zamudio said. "This is surprising. It [Steffey's death] makes you wonder if this is a safe neighborhood."
Another neighbor, Cody Sorensen, also said Steffey liked to talk to the neighborhood children. His neighbor had gotten rid of her car after her husband died, Sorensen said, and he saw her get on the bus every morning.
Matthew and Erica Parker, who also live on Steffey's street, said she kept mostly to herself but was friendly when encountering people.
"She was always smiling," Erica Parker said.