Ronnie "Jay" Adrian Towns, 28, also was charged with armed robbery, the Telfair County Sheriff's Office said on its website. A judge denied bail for Towns, who also waived his right to a preliminary hearing.
After Towns' initial appearance, reporters shouted questions as he was led from the courthouse, but the suspect remained silent.
The victims were shot in the head, police said.
Elrey "Bud" Runion, 69, and his wife, June, 66, had driven three and a half hours from an Atlanta suburb in search of a classic car after posting on the popular want-ad website. Their bodies were recovered Monday in woods in rural Telfair County.
An autopsy Tuesday confirmed their identities.
Towns turned himself in Monday.
His father told CNN affiliate WSB
on Tuesday that his son said he was innocent.
"He said, 'Daddy, I ain't had nothing to do with this,' " Ronnie Towns Sr. told the station. "It ain't Jay. I don't believe he did it."
The suspect's father told WSB that he went into the woods Monday where Towns was hiding and talked him into surrendering. His son had no prior record, he said.
In search of a vintage Mustang
Telfair County Sheriff Chris Steverson said Towns had the "last known communications" with Bud Runion.
The couple made the trip to look at a 1966 Mustang, and once Runion got to Telfair County, the suspect communicated with him, according to the sheriff. He did not say who called whom. McRae is about 180 miles from Marietta, where the Runions lived.
"Early on in the investigation, we did contact Mr. Towns, and we did interview him and by the information he provided, we found it to be false and deceptive," the sheriff said shortly before Towns turned himself in. "After we interviewed him, our efforts to contact him were unsuccessful. Today we've contacted his family, and they've been helpful in locating him."
Neighbors pay respect
At the victims' home in Marietta, people placed flowers at a memorial around a flagpole in the front yard. A neighbor had lowered the flag to half staff.
Another neighbor brought a child's bicycle. He said Bud Runion used to fix bikes through a church group for children in need.
"Bud is a veteran. He and June are great people. They give so much; they are selfless," Josh Patterson, the couple's son-in-law, said Monday.
Site has history
Though the overwhelming majority of Craigslist transactions occur without incident, the site has a history of being co-opted by criminals.
Just in recent years, there have been numerous such instances. In Henderson, Nevada, police said a man placing an ad in July
met three men at a park, who took him to a vacant house, tied him up, beat and robbed him, then escaped in his car.
In March, a San Jose, California, woman responding to an ad for a cellular phone was allegedly kidnapped at gunpoint
by two men who drove her to an ATM and demanded her passcode, police told a newspaper.
In May 2013, a Maine teenager drove to Portland to sell his BMW sedan to a 29-year-old who had responded to his Craigslist ad. The teen was allegedly forced into his own trunk and driven to Delaware, according to media reports
and an FBI affidavit