The 29-year-old mother had been last seen sometime on Thanksgiving Day, placing her 1-year-old daughter in a shopping cart and strolling into a supermarket near their home in central Colorado.
It was never clear why Kelsey Berreth needed to make a stop at that Safeway near Woodland Park, Colorado.
And it was never clear where she went after she finished shopping for groceries, though her fiance, Patrick Frazee, later told investigators that the couple had met up at some point to exchange their daughter.
The only thing was that was certain was that Berreth had vanished - and no one could seem to find her.
But now - a month after she went missing - Frazee, her fiance, has been accused in her death, authorities said.
Woodland Park Police Chief Miles De Young said during a news conference Friday morning that Frazee, 32, has been arrested on suspicion of first-degree murder in connection with her death.
De Young said that following numerous interviews over the past several weeks, investigators had gathered enough information to file for an arrest warrant. Although police have still not found her body, the chief said that they do not believe she is alive.
The couple's daughter, who has been with Frazee, is now in protective custody, according to authorities.
Frazee's attorney, Jeremy Loew, did not immediately respond to a request for comment from The Washington Post.
It was Dec. 2, 10 days after Berreth's disappearance, that her family reported she was missing. On Nov. 25, three days after she had vanished, text messages were still being sent from her phone - one to her fiance and one to her employer, explaining that she would not be showing up for work, police said. The phone pinged near Gooding, Idaho, about 800 miles from her home, police said.
Throughout the investigation, authorities were stressing that it was still considered a missing person case.
Meanwhile, Berreth's family members were posting pictures and messages about the young mother on social media, offering the information they had and pleading with the public for help.
"She's not the kind that runs off. This is completely out of character," her mother, Cheryl Berreth, said at a news conference earlier this month. "Kelsey loves her dog, she loves her family and friends, and she loves her job. She's reliable, considerate and honest."
Then, through tears, she pleaded with her daughter to try to call home.
"Kelsey, we just want you home," she added. "We won't quit looking."
After Frazee's arrest Friday morning, authorities said that Berreth's family would not be commenting.
De Young, the police chief, told reporters during the news conference that investigators pored over cellphone records and other data, and conducted numerous searches at Berreth's home, where they recovered "a number of items that made us suspicious that the crime did occur at Kelsey residence." Police said they are still searching for her body.
Frazee was arrested on suspicion of first-degree murder and solicitation to commit murder, records show. Police did not elaborate on the solicitation charge but said there have been no other arrests.
The couple's daughter will be reunited with Berreth's family, police said.
"Our work is just beginning," De Young said of the case, promising a "relentless pursuit of justice for Kelsey and her family."