OAKLAND -- A 39-year-old woman was killed Saturday night and her boyfriend wounded when a gunman opened fire on their car while they were on their way to a fast-food restaurant, police said Sunday.

The woman's 5-year-old son, who was also in the car, was not wounded but was taken to the hospital as a precaution, police said. The couple was stopped in the car at the corner of 72nd and Lacey avenues at about 9:40 p.m. when a gunman approached on foot, according to police. After a brief exchange of words, the gunman began firing.

The 23-year-old boyfriend, who was wounded in the shoulder, was able to drive away but crashed into a fence and a pole in the 7200 block of MacArthur Boulevard. The woman was pronounced dead at the scene. The couple, who had been together for three years, live near where the shooting took place, police said. The child is now in the custody of Child Protective Services.

The shooting occurred a few blocks away from the Eastmont Police Substation. Investigators have not identified a motive or a suspect, according to Officer Eric Milina.

Police and Crime Stoppers of Oakland are offering a $20,000 reward for information leading to the arrest of the gunman. Anyone with information on the case is asked to call 510-238-3821 or the tip line at 510-773-2805.

Harry Harris and David DeBolt cover breaking news. Follow them at Twitter.com/harryharris15 and Twitter.com/daviddebolt.