Marty Thomas Gibson's body was found in Lake Olmstead on Thursday. SPECIAL

Marty Thomas Gibson, 48, was last seen at 3 a.m. Thursday outside his Eve Street home, where neighbors saw him drinking heavily. Five hours later, fisherman William Badger found him a mile away, floating facedown in the lake near the Broad Street bridge.

Authorities at the Richmond County Sheriff's Office say they don't believe he went for a late-night swim.

"We're treating the case like a homicide because of evidence we found at the scene," Maj. Ken Autry said, declining to discuss specifics.

Mr. Gibson, who lived at home with his father and step-mother, was mentally disabled and suffered epileptic seizures, relatives said. He liked to swim, but he usually went in the river near his home.

Mr. Badger found him dressed only in blue-jean cut-off shorts with two inhalers, cash and an identification card in his pockets. Police later found shoes and a shirt on a hill nearby that matched the description of clothing Mr. Gibson was last seen wearing.

There were no visible signs of trauma on the body to indicate how he died, police said. Coroner Leroy Sims pronounced him dead at 9:05 a.m. at the lake, and his body was sent to the state crime lab in Atlanta for an autopsy. A cause of death is expected to be known today, Mr. Sims said.

EMT and fire rescue workers lift the body up the embankment from Lake Olmstead at the Broad Street bridge. William Badger, a fisherman, discovered the body Thursday morning. ANDREW DAVIS TUCKER/STAFF

Mr. Badger, of Hephzibah, said he had just put his boat in the lake and was near the Broad Street bridge about 8:30 a.m. when he spotted the body floating in the water not far from land.

"You couldn't miss him," he said.

The fisherman then landed his boat under the bridge and yelled to two women walking nearby to call police.

Reach Greg Rickabaugh at (706) 828-3851 or greg.rickabaugh@augustachronicle.com.