The man who admitted to keeping a missing 7-year-old girl against her will in his apartment and later killing her knew the girl's family, police said.

Esar Met, 21, was booked on charges of aggravated murder, kidnapping and evidence tampering after confessing to the crime.

Police on Tuesday night found the body of Hser Nay Moo, who disappeared Monday from the apartment complex after an argument with her 10-year-old brother. Hser's body was found in the bathroom of Met's basement apartment, which is in the same complex where her family lives, MyFOXUtah reported.

Hser was killed within an hour of when she left her home, South Salt Lake Police Chief Chris Snyder said at a press conference Wednesday.

Hser went to Met's apartment, where she often played, according to police.

"We do not know how she got in, whether or not she was invited in or whether or not she asked to go in," Snyder said.

Met hid the body and left the apartment after a physical altercation with Hser that led to her death, Snyder said. Snyder would not release Hser's cause of death or if she was sexually assaulted.

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Met admitted to authorities to confining Hser in the "residence by force, resulting in her death," as well as to trying to conceal the body, according to a Salt Lake County jail document.

Click here to read the probable cause statement (pdf).

Met had lived in the apartment for 30 days. He does not have a criminal record in the U.S.

Police found Hser's body in a South Parc apartment after obtaining a search warrant, MyFOXUtah reported. Four other people living in Met's apartment were taken into custody but later released. They are not believed to be involved in Hser's death, Snyder said.

Cartoon Wah, Hser's father, said through an interpreter that he was thankful to the public for their support.

"I have one daughter in this world, and I loved her the most," Wah said.

Wah, a Burmese immigrant who came to the United States last year, has five children. Hser was his only daughter.

More than 800 people searched for Hser and investigators went without sleep in hopes of finding the little girl alive.

The Associated Press contributed to this report.