Timothy Cunningham, an epidemiologist at the CDC, was found in Chattahoochee River in northwest Atlanta late Tuesday. Fishermen in the area spotted the body along the bank of the river face up. The decomposed body was stuck in mud in an area that was not easily accessible, leading officials to believe it was "in that position for a while." 

"We have no indications to this point that were was any foul play," Atlanta Police Department Major Michael O'Connor said in a Thursday news conference. 

It's unclear how Cunningham's body ended up at that part of the river. An official cause of death has yet to be released, but a preliminary autopsy suggested the 35-year-old drowned, the medical examiner said at the Thursday news conference.

Three crystals were found in Cunningham's pockets when his body was recovered. Cunningham, who was last seen leaving work early on Feb. 12, was an avid crystal collector. The ones found on Cunningham were described as "rare crystals."