An investigation of the Wednesday incident found Stephanie Hicks, 20, of Alton wrestled an Alton city police officer's pistol away from him and shot herself, the St. Louis Post-Dispatch reported.
Officer Rick Eckhard of the St. Louis County police across the Mississippi River from Alton, said Friday the shooting appeared to be a suicide.
"This is believed to have occurred after a struggle over the control of the Alton police officer's weapon while in the patrol vehicle wherein [Hicks] was shot in the head and died as a result of her injury," Eckhard wrote in a statement.
Alton Police Chief David Hayes said the officer, whose name was not reported, followed proper departmental procedures when he responded to "a domestic issue going on between" Hicks and the person who called police. Hicks was attempting to walk to a hospital and did not appear to be suicidal when the officer arrived at the scene.
The officer was given permission by the watch commander to give Hicks a courtesy ride and allow Hicks to ride in the front seat, as she was not in custody.
Hayes said Hicks "never said a word" while she was in the car. Then, at some point, Hicks grabbed the officer's weapon and a struggle ensued. Hicks ended up shooting herself in the head and was transported to Barnes-Jewish Hospital in St. Louis, where she died.
The officer, who was not injured, was placed on administrative leave.
Hayes said an internal investigation would start after St. Louis County police finish their investigation of the death.