Police found a 28-year-old shot in the chest outside a home on the 7200 block of Walker Street.
Investigators say two men were fighting over a girlfriend when the victim broke through the rear door of the home after being locked out and confronted the roommate with a knife.
The roommate then allegedly fired shots, hitting the victim, who stumbled outside.
He is hospitalized in critical condition.
The roommate stayed at the scene and is cooperating with the police.