A witness first called 911 at about 7 p.m. after finding the boy in the parking lot of a shopping center in the 4500 block of Klahanie Drive. The car was locked and the windows were rolled up, according to Cindi West of the King County sheriff's office.
West said the witness went into several nearby stores looking for the owner of the car. When nobody claimed the car or the boy inside it, a store employee announced the information over a public address system.
Deputies arrived moments later and a sergeant immediately grabbed a hammer from his patrol, smashed out a window and rescued the boy.
West said the boy was lethargic and slow to respond when he was finally freed from the hot car. He was taken to a local hospital for treatment.
The father eventually returned to the car and was promptly arrested and booked into King County Jail on suspicion of second degree child endangerment. The man told deputies he left the baby in the car for about 20 minutes.
Deputies notified Child Protective Services and the baby was returned to his mother.