Police say it happened around 5:38 p.m. at Clem's Garage on 5170 Main Street. They say two men were found shot in the business parking lot.
Burley Puffinberger, 24, of Stephens City, Virginia, was declared dead at the scene.
Charles Jenkins, 56, of Toms Brook, Virginia, was taken to Winchester Medical Center. He was later pronounced dead at the hospital.
Investigators say a fight between Puffinberger and Jenkins escalated to the point where Puffinberger retrieved a firearm from his house and began shooting at Jenkins and two other people at the scene.
Investigators say it appeared Puffinberger followed Jenkins through a parking lot, shooting him at least twice. They say Puffinberger missed the two other people he was shooting at, and within seconds of killing Jenkins, Puffinberger took his own life with a single gun shot.
Investigators say Jenkins was Puffinberger's father-in-law. Witnesses say there was a negative history between the two.
The Stephens City Police Department and the Frederick County Sheriff's Office say the crime scene was processed and findings will not be complete until all forensic and ballistic evidence is analyzed.