Police released 911 calls from the moments after the shooting, including one from the man claiming he was robbed.
"As soon as I unlocked the phone, the other guy acted like he was reaching for something. That's when my wife did what she had to do," the man told a 911 dispatcher.
"Did the person who robbed you have weapons?" the dispatcher asked.
"We think so because he came out with his shirt up like something was under his shirt," the man said. He added later: "We discharged our firearm on them when I thought he was pulling a firearm on me."
Police said the couple left the scene for fear of retaliation. Williams' lifeless body was found inside a burgundy car along Jefferson Street moments later.
The husband and wife, whom police have not yet identified, are cooperating with the investigation, police said.
Police have not said if Williams was armed or if they believe the shooting was justified.