Copson said there are two retention ponds on either side of the tracks and "the area where he was found was only about three feet deep."
"There was no sign of any kind of trauma or any kind of struggle," Copson said. The investigation has uncovered no signs of foul play, he added.
Frost said there were "tiny faint bruises" on Robinson's elbows and on the side of his neck, but no traumatic injuries.
Robinson and his girlfriend were visiting friends at Royal Crest Estates on Friday. She told Copson that Robinson left at about 10 p.m., telling her he was going to walk down the railroad tracks to a relative's house.
Copson said the autopsy put the time of death as Friday night.
Robinson, who lived with the woman at Kountry Kove Apartments on U.S. 11 south of Martinsburg, had not been reported missing to police.
"She was looking for him all weekend," Copson said of the girlfriend. She went back to Royal Crest Estates Monday because that was the last place she had seen him.
The area around the pond "is not a well-traveled area," Copson said.
Frost said he will not issue a death certificate until toxicology tests at the chief medical examiner's office in Charleston, W.Va. He said he would be taking blood samples to the lab today to determine whether drugs and alcohol were contributing factors.
Those test results may not be available until after Christmas, Frost said.
The girlfriend told Copson that Robinson was a self-employed carpet cleaner.