A St. Louis police officer �mishandled� a gun and accidentally shot and killed a colleague early Thursday, authorities said.

The shooting happened around 1 a.m. at an officer�s home, police Chief John Hayden told reporters during a news conference shortly after the shooting. Two on-duty male officers were at one of their apartments when Katlyn Alix, who was off duty, stopped by, according to police.

A police incident report said the three officers were seated in the apartment living room when one of the male officers �mishandled a firearm and shot (Alix) in the chest.� The male officers, both 29, drove Alix, 24, to a hospital, where she died.

Hayden declined to answer questions about the circumstances surrounding the shooting or why the officers had gathered at the home. He did say that the officers� arrival at the home was not proceeded by a call for service or help.

Police have not released the names of the male officers. Police have not said whether the gun involved was a service weapon.

An internal police investigation is underway, and the male officers are on paid leave during that probe. The St. Louis Circuit Attorney�s Office is also investigating and has asked the Missouri State Highway Patrol for help. Susan Ryan, a spokeswoman for Gardner, said the request was not out of the ordinary.

Mayor Lyda Krewson on Twitter called the shooting �terribly sad.�

�Officer Alix was an enthusiastic and energetic young woman with a bright future ahead of her,� Hayden said in a statement.

The department said Alix was a patrol officer who had graduated from the St. Louis Police Academy in January 2017. Alix, who was also a military veteran, is survived by her husband, parents and a sister.

Jeff Roorda, business manager of the St. Louis Officers Association, said in a statement that the fallen officer �served her community and her nation with dignity and courage both as a police officer and as a member of the military.�

Roorda said the union understands that the media and the public want more information.

�So do we,� Roorda said. �But for now, we wait; we wonder; and we weep.�

(AP)