Don Wiley, 57, had been missing since Nov. 16, when his rental car was found abandoned with the keys in the ignition on a Mississippi River bridge at Memphis.
Wiley's disappearance had raised concerns about a possible terrorist connection since he had done research on a number of potentially deadly viruses, including Ebola, a highly contagious and lethal fever.
The FBI said it was leaving the investigation to the Memphis police. Authorities have disclosed no evidence of connection between Wiley's work and his disappearance.
The body was discovered Thursday snagged on a tree near a hydroelectric plant at Vidalia, La., across the river from Natchez, Miss, about 300 miles south of Memphis. A wallet containing Wiley's identification was found on the body, police said.
Shelby County medical examiner O.C. Smith began an autopsy on the body Friday. The body was identified through dental records, police Lt. Walter Norris said.
Authorities said the cause of death may be determined in the coming week. No evidence of foul play was found in the car.
Members of Wiley's family declined comment Saturday.
Wiley was in Memphis for a scientific conference hosted by St. Jude Children's Research Hospital. He was last seen publicly at a conference banquet, and colleagues said he showed no evidence of emotional distress.
He was very upbeat, very engaging and in great spirits, said Jerry Chipman, a St. Jude spokesman.
Scientific organizations, including St. Jude, posted rewards totaling $26,000 for information leading to the arrest and charge of anyone responsible for Wiley's disappearance.
© MMI, CBS Worldwide Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report