Surveillance video showed a man reaching into a display case at the "Elvis After Dark" exhibit at Graceland, Presley's mansion, and removing a black, 9 mm Smith & Wesson pistol on Aug 14.
Travis Brookins turned the gun over to police Monday after the theft was reported by news media.
Brookins said he was cleaning portable toilets behind the exhibit hall last Thursday when he found the gun in the muck. Unaware the weapon had been stolen, Brookins took it home and cleaned it.
"He called us and said he thinks he had the gun and brought it to us," Memphis police Lt. Jerry Gwyn said.
Gwyn said he believes the thief may have accidentally dropped the gun into the toilet.
"Of course, whoever dropped it wouldn't go in there," he said.
Presley died at Graceland on Aug. 16, 1977, and is buried in a small garden beside the house.
Tens of thousands of fans were in Memphis last week for various ceremonies marking the anniversary of Presley's death.