A 6-year-old girl reported missing by her father this week may actually have been killed more than a year ago, police said, and they called the father a "person of interest" in the case.

The search for Aarone Thompson was suspended, and police opened a homicide investigation on Thursday, following a tip that someone killed her at her home, interim Police Chief Terry Jones said.

There were no arrests by early Friday.

Aaron Thompson reported his daughter missing on Monday, telling police she left after an event that upset her. That was a lie, Jones said, declining to elaborate.

Jones called Thompson a "person of interest" and said police planned to interview him and his live-in girlfriend.

"The investigation leads right back to this home," Jones said during a news conference. "We believe that Aarone is no longer alive and that suspicion is rising to the highest level."

Jones said that although Aarone's 7th birthday is Nov. 30, police didn't find any pictures of her older than 4 1/2 as they searched for her with dozens of officers, dogs and aircraft. The child also wasn't enrolled in school.

"Over a period of time — up to possibly a year and a half ago — Aarone Thompson may have been murdered," Jones said.

Thompson had made an impassioned plea for his daughter earlier this week. "I'm scared for her safety. ... If anybody has information, please contact the police to bring my baby girl home," he told KMGH-TV.

The girl's mother, Lynette Thompson, who is staying in a homeless shelter in Detroit, has said she believed Aarone (pronounced air-un-AY) is a crime victim.

"What does a 6-year-old know about running away?" she told the Aurora Sentinel & Daily Sun. She has said the split with her husband was bitter and she hasn't seen the child since 2001.

Police said Aaron Thompson was uncooperative during the initial search. Sam Riddle, a family friend and spokesman, did not return a phone call from The Associated Press but told Denver television stations that the family has answered questions from investigators, let them search the home and gave DNA samples and fingerprints. He faulted police handling of the case.

Investigators could be seen late Thursday walking in and out of the family's home, which is surrounded by a neat yard in a cul-de-sac. Seven other children who live at the house, ranging in age from 6 to 15, have been placed in protective custody, Jones said.

Veronica Boivin, who lives a few houses away, said she rarely saw any children outside the home, except for going to and from school or doing yard work.

"I don't ever remember seeing that little girl. I remember older kids," she said. "They're always cooped up into their home."

Near the home, someone had tied a handwritten sign and an artificial yellow rose to a fence. Beneath it were a candle and a stuffed, white unicorn.

"Aarone we all miss you," the sign said. "We all love you. Please come home."