The shootings took place around 5:30 p.m. at the Gravois Place apartment complex in the 7400 block of Gravois Avenue.
Police said a woman in her 60s was found shot to death in the hallway right outside the door to her apartment. The door was left open. A man around the same age was found with a gunshot wound to the chest. He was rushed to a local hospital in critical condition.
It's unclear if the pair were married or related.
There were no signs of foul play, no evidence of a break-in, and no one saw a third person leave the scene.
This is St. Louis City's ninth homicide in 2018.