An officer on patrol discovered the bodies about 6 a.m. after noticing broken glass next to the car.
Seattle police spokesman Mark Jamieson said it appears the two men had been shot in the head and the gunman remains on the loose.
Investigators cordoned off the area near the intersection of 39th Avenue South and Kenyon Way while they collected evidence.
Family members identified one of the victims as 34-year-old Edward Westmoreland.
"We loved him deeply," said the victim's father, also named Edward Westmoreland. "He loved his family deeply, especially his son."
The victim's son was just 6 years old.
"He was with his dad yesterday learning how to ride a bike," said the boy's mother. "That was his last memory -- his dad showing him how to ride a bike."
Police marked a path of blood on the sidewalk, which may reveal the gunman's path. Investigators say it appears the shooter may have fired from close range and then walked along the sidewalk to a getaway car.
Court documents reveal the victim has a long criminal record, but his father said he was getting his life together.
"He was getting on track, getting closer with his son," the elder Edward Westmoreland said.
He says he believes his son's death is about easy access to guns.
"Edward didn't deserve to be a victim of violence, he really didn't."
Police have not identified the second victim.