The door to Botham Jean's apartment was unlocked, according to an arrest warrant affidavit released Monday, and officer Amber Guyger entered the unit, believing it was her own.

More details are emerging about what officials say happened during the fatal encounter between Dallas police officer Amber Guyger and Botham Jean, who was killed at his South Side Flats apartment last week.

The door to Jean's apartment was "slightly ajar," according to an arrest warrant affidavit released Monday, and Guyger – who lives in the apartment directly below Jean – entered the darkened unit, believing it was her own.

The affidavit was written by an investigator for the Texas Rangers, which took over the case at the request of Dallas police.

An earlier search warrant affidavit written by a Dallas Police Department detective said that Guyger was trying to enter Jean's apartment when Jean "confronted the officer at the door." The DPD affidavit also said that Guyger later told investigators the apartment door was open when she placed her key in it.

A neighbor told police that he "heard an exchange of words, immediately followed by at least two gunshots," the DPD affidavit said.

According to the Rangers' affidavit, Guyger inserted a key into the door, fully opening it, and then she saw a "large silhouette" across the room, believing it was a burglar.

Guyger then drew her firearm, and yelled commands at Jean, according to the affidavit. Jean "ignored" the commands, so Guyger fired her gun twice, striking Jean, the affidavit said.

Guyger told investigators that Jean moved toward her, sources told WFAA.

Guyger had gone to the wrong apartment after parking on the fourth floor of the South Side Flats apartments, the affidavit said.

Guyger, a four-year veteran of the force, was arrested on a manslaughter charge in the case Sunday. She posted $300,000 bond and was released from custody shortly after she turned herself into the Kaufman County Jail.

The case is still under investigation, both by the Texas Rangers and the district attorney's office.

District Attorney Faith Johnson spoke at a news conference Monday morning and said her office is "independently" looking at the case.