Dr. Timothy Cunningham, 35, had not been seen since Feb. 12, when he left work early after complaining of feeling sick. It came after he had been passed over for a promotion he had sought, according to police.
Officials at the Centers for Disease Control and Prevention have denied he was overlooked for a higher position.
His body was pulled from the river late Tuesday. Atlanta police said Thursday that Cunningham's cause of death was drowning and there was no evidence of foul play.
But the disappearance of the Harvard-educated epidemiologist was previously described as "unusual" by authorities.
The well-liked scientist left behind his dog, Mr. "Bo" Bojangles, along with his wallet, keys and cellphone, police said. His car was parked in the garage and his yellow home was locked.
"This is an extremely unusual set of circumstances. Every single belonging we were aware of was located in the residence," said Atlanta Police Department Maj. Michael O'Connor at a Feb. 27 press conference.
"It is not common in missing-person cases for us to find someone's entire belongings," he said.
At a media conference Thursday, O'Connor said, "We may never be able to tell you how he got into the river."
Cunningham's body was found by two fishermen who phoned 911 to report a corpse mired in mud and water along the riverbank. Authorities described the area as rugged and not easily accessible by car or walking trails.