The man who shot and killed Joe McKnight is a 54-year-old white male named Ronald Gasser ... the Jefferson Parish Sheriff's Office tells TMZ Sports.
Law enforcement says Gasser is currently detained and being questioned about why he shot the 28-year-old football star.
At this point, he has NOT been formally arrested.
Cops say Gasser stayed at the scene of the shooting until cops arrived. Once law enforcement got to the scene, he handed over his gun without further incident.
Cops say they're investigating the shooting as a road rage incident -- and are trying to find out what happened in the moments before the former NY Jets running back was killed.
Story developing ...