Kelsey Berreth, 29, of Woodland Park, Colorado, was last seen shopping for groceries on Thanksgiving Day. Police said the only signs of Berreth after Thanksgiving were some text messages and that location data suggested the phone by November 25 was near Gooding, Idaho, 800 miles (1,290 kilometers) from her house. Berreth, who shares a one-year-old daughter with Patrick Frazee, has been missing since Thanksgiving. Frazee's arraignment has yet to be set, May said.
She said the couple had weathered some financial struggles.
"Sadly, we do not believe Kelsey is alive", De Young said, adding that officials have narrowed down their search.
Police started looking for Berreth on December 2 after her mother, Cheryl, asked for a welfare check.
Berreth's mother repeatedly squashed speculation about her daughter's fiancé, as did police and his attorney.
Frazee's attorney, Jeremy Loew, said last week his client "continues to cooperate with law enforcement in the missing person investigation". The child had been staying with Frazee but is now in protective custody, De Young said.
On Friday, De Young did not say when or how Berreth may have been killed but noted that investigators have recovered a "number of items" suggesting she was killed at her Woodland Park residence. District Attorney Dan May would not elaborate on the circumstances behind his being charged with solicitation to commit murder, but said that it is a crime to solicit somebody to commit another crime.
But authorities declined to say whether they had found the body of Kelsey Berreth, 29, what led to the arrest of Patrick Michael Frazee and what motive there might be for Berreth's disappearance and slaying. Officials were able to get the arrest warrant based on the interviews they conducted with Frazee.
Frazee previously said he saw Berreth on Thanksgiving Day when she dropped off their 1-year-old daughter, according to authorities.
According to property records, Ms Berreth purchased her single-family home in Woodland Park in May.
Berreth's phone was tracked to a location near Gooding, Idaho. De Young said police do not know whether additional arrests will be made in the future. Gooding is roughly 800 miles northwest of Woodland Park.
The criminal affidavit in the case has been sealed until investigators can follow up on leads and feel confident the release of documents won't hurt the investigation, May said. Federal Bureau of Investigation agents, meanwhile, were at the home of Berreth in Woodland Park on Wednesday and again on Thursday night. "This is completely out of character". Kelsey loves her God, she loves her family and friends, and she loves her job. "She's reliable, considerate and honest". Berreth's cousin, Jodi Garretson, told Inside Edition her family was "absolutely devastated" by the news that authorities do not believe Berreth is still alive.