The shooting began just before 1 p.m. Tuesday when Senior Police Officer Tony Howard stopped a Chevrolet Suburban, authorities said. The passenger got out of the SUV and shot and wounded Howard.
The driver was arrested, but the passenger ran and encountered another senior officer, Elmer "Buddy" Christian. Police said the passenger shot and killed Christian in his patrol car.
The suspect has been identified as 33-year-old Jamie Hood. Police said a reward of $50,000 is being offered for his arrest.
The FBI contacted the Georgia Bureau of Investigation Wednesday to say they were adding $40,000 to $10,000 already offered for information leading to Hood's arrest.
"I believe $50,000 is a good incentive for someone to come forward and offer up Jamie Hood for arrest," GBI Director Vernon Keenan said.
Howard underwent surgery and is expected to recover, police said, but have not provided details.
After the shooting, police fanned out along a major highway and conducted a house-by-house search for Hood..
The search Wednesday morning apparently shifted east, prompting Oglethorpe County school officials to place schools on lock-down.
The shootings came on the same day police chiefs from around the country said they supported longer prison terms for gun-carrying felons as a way to combat a recent rise in line-of-duty deaths. U.S. Attorney General Eric Holder, also saying he was worried about the rise, directed U.S. attorneys nationwide to identify repeat offenders for possible prosecution under federal law that would make them eligible for stiffer sentences.
A total of 162 officers died in the line of duty last year, up from 117 in 2009. Before the Georgia shootings, so far this year, 49 lost their lives, a 20 percent rise from the same time last year.