The 3-year-old girl fatally shot in Southeast D.C. Wednesday night was accidentally shot by her 7-year-old brother, according to the Metropolitan Police Department.

Dalis Cox, her brother, their mother, an unrelated adult and a teenager were inside a second-floor apartment on the 600 block of 46th Place SE in Benning Ridge when the little girl was shot just after 8 p.m. Wednesday, police said.

"We believe it was a young child that got their hands on the gun," D.C. Police Chief Cathy Lanier said at a news briefing Thursday afternoon, noting the firearm was not registered. "We believe it was an accident."

Police are investigating whether the gun was brought into the home by the teen, whose sex and age were not immediately revealed.

"We have the gun. It is not a registered," legal gun," D.C. Mayor Muriel Bowser said. "We haven't determined how the gun got in the house."

The child was rushed to Prince George's Hospital Center in critical condition by D.C. police who were already on the scene, Lanier said. Dalis was pronounced dead late Wednesday.

Police later confirmed that Dalis's brother fired the shot.

No one has been charged in connection to the child's death.

"We have to figure out where the gun came from, how it got in the house," Lanier said. "If there’s any criminal liability, someone will be charged."

Asked if other firearms were found in the home, Lanier declined to comment.

Dalis's devastated father, Timothy Cox, told News4 he dropped off his daughter at her mother's apartment Wednesday night.

"I told her I had to go to work -- 'I'll pick you up tomorrow,'" he said.

Just 30 minutes after Cox left, he received a call telling him his child had been shot.

"I loved her with all my heart. It's tough to have a 3-year-old daughter just being taken," he said.