HAVRE, Mont. >> When Alicia Navarro disappeared in 2019 from her home in a Phoenix suburb days before her 15th birthday, she left a signed note for her family promising she would return.

“I will be back, I swear,” the note read. “I’m sorry.”

Believing she would keep her promise, Jessica Nunez never stopped searching for her daughter.

She paid for a billboard ad in Mexico that featured a photo of her daughter for a year. She bought 10 more ads in Las Vegas. She spoke at events and gave media interviews to raise awareness. She left flyers all around Glendale — at salons, truck stops and parks.

Nunez’s yearslong search came to an end Sunday when her daughter, now 18, walked into a small-town Montana police station near the Canadian border and identified herself as the missing teenager.

Police said Navarro told them she hadn’t been harmed, wasn’t being held, and could come and go as she pleased. She does not face any criminal charges, they added.

Investigators are now trying to determine what happened to Navarro after she disappeared and how she ended up in Havre, Montana, more than 1,300 miles (2,090 kilometers) from her home.

Over the years, Nunez had raised concerns that Navarro, who was diagnosed with autism, may have been lured away by someone she met online.

Authorities in both Montana and Arizona haven’t said how long they believe Navarro was in Havre before walking into the police station. Glendale police Lt. Scott Waite said at a news conference Wednesday they were looking into all the possible scenarios that could have led to Navarro’s disappearance, including kidnapping.

In Havre — a town of about 9,200 people surrounded by farmland and north of the Rocky Boy’s Indian Reservation — Navarro’s story had residents buzzing even though most had never seen or heard of her. It also piqued interest when a team of heavily armed law enforcement officers entered an apartment and took a man into custody just a few blocks from the Havre police station Wednesday night, witnesses told The Associated Press.

As many as 10 uniformed and undercover officers showed up at about 8 p.m. and took him away in handcuffs. He had been living in the apartment, said Rick Lieberg, who lives across the street.

A young woman later emerged from the apartment who Lieberg said he had not previously seen. The woman resembled a photograph of Navarro that was released by police, he said.

Jonathan Michaelson, who lives next door, said he was questioned Wednesday night by a plainclothes police officer from Arizona who asked whether he had ever seen a girl at the apartment next door. He said he had not.

“If she was in that apartment, I’m surprised I never saw her,” Michaelson said.

But officer Gina Winn, a spokesperson for the Glendale police, said this morning that no one has been taken into custody in the disappearance of Alicia Navarro. Winn declined to say whether investigators know how long Navarro was in Montana or how she ended up there. No one answered the door this morning at the apartment, one of six units in an aging building in a residential neighborhood.

A person who works at the Dollar Tree in Havre, Jeff Hummert, said he saw a young woman resembling a photograph of Navarro last year in a city park two blocks from the apartment raided by police Wednesday. She was walking alone and carrying a plastic Walmart bag, Hummert said.

Nunez declined an interview request. But for years, she had documented her efforts to find her daughter on a Facebook page titled “Finding Alicia.”

In an emotional video viewed more than 200,000 times since it was posted Wednesday, Nunez told her tens of thousands of followers: “For everyone who has missing loved ones, I want you to use this case as an example. Miracles do exist. Never lose hope and always fight.”

Nunez had amassed a loyal following on social media throughout the years while sharing inspirational quotes, photos of Navarro as a young child and posts addressed directly to her daughter.

“Alicia I know you will fulfill what you promised,” Nunez wrote in one post. “You will be back.”

People across the U.S. reached out to the Arizona mother to ask how they could help, creating an informal network of volunteers. They shared photos and information through the Facebook page.

Glendale police said this week that they received thousands of tips over the years.

In a short video clip that Glendale police said was taken shortly after Navarro arrived at the Montana police station, she can be heard telling authorities, “No one hurt me.” In another short video, Navarro thanked the police.

“Thank you for offering help to me,” she said.