The Dallas police officer who killed 26-year-old Botham Jean in his own apartment got inside because the door wasn’t locked, a law enforcement official said Sunday.

Officer Amber Guyger had just ended a 15-hour shift when she parked on the wrong level of the South Side Flats garage— the fourth floor instead of the third, where she lived, according to the official who has direct knowledge of the case but is not authorized to discuss it publicly.

Dallas Mayor Mike Rawlings also said Sunday that Guyger parked on the wrong floor.

Amber Guyger

She went to the door she thought was hers but was one floor too high. The four floors of the South Side Flats in the Cedars look the same, with concrete floors and tan doors. A light fixture to the side of each door displays the apartment number.

Guyger, 30, was arrested Sunday on a manslaughter charge and was booked into the Kaufman County Jail. The Texas Rangers are investigating the case at the request of Dallas Police Chief U. Renee Hall. In the last year, juries have sentenced two police officers in Dallas County to prison time after convicting them of murder.

The night of the shooting, Guyger didn’t notice that Jean's door had a red doormat in front of it, the official said. Her entrance didn’t have one.

Guyger, who was still in uniform, put her key in the door, which was unlocked, and the door opened, the official said. The lights were out. She saw a figure in the darkness and thought her apartment was being burglarized, the official said. Guyger pulled her gun and fired twice.

When she turned on the lights, she realized she was in the wrong apartment. Jean, who worked for PricewaterhouseCoopers, was shot once in the chest.

Authorities have said Guyger and Jean, a native of Saint Lucia in the Caribbean, did not know each other. Guyger, a nearly five-year veteran of the Police Department, had recently moved into the complex.

A light fixture to the left of Botham Jean's door identifies his apartment number. Dallas police say that an off-duty officer, Amber Guyger, on Thursday shot and killed Jean when she mistakenly thought his apartment was hers. (Jennifer Emily / Staff)

Guyger called 911 crying, the official said. She repeatedly said, “I thought it was my apartment” and apologized to Jean.

“I’m so sorry,” she can be heard saying on the recording of the 911 call, the official said. Police arrived within four minutes.

A video taken by someone at the apartment complex shows Guyger in the hallway crying and pacing with a phone to her ear.

The video shows paramedics rushing by with Jean on a stretcher as a paramedic kneels on top of him, performing chest compressions.

Jean, who is remembered as someone who "loved mankind," was pronounced dead at Baylor University Medical Center.

Correction 2 a.m.: A photo caption incorrectly referred to a murder charge, rather than a manslaughter charge.