Fetterhoff, 58, of Grant Street in Greencastle, clung to life Tuesday in the intensive care unit at Washington County Hospital. He was listed in critical condition.
Investigator Roy L. Harsh said Fetterhoff apparently remained for a week after the beating along the Conococheague Creek east of the Creek Bridge on Broadfording Road. When he was discovered at about 3 p.m. Monday by a fisherman looking for bait, he was unconscious, Harsh said.
"I can't imagine anyone lying there unconscious day and night for a week and being able to survive that. He's very fortunate," Harsh said.
Investigators spent much of Tuesday preparing charges against Thomas and piecing together a case that began as a missing person report a week ago. Harsh said Fetterhoff dropped his wife off at work last Wednesday morning and then drove to Hagerstown and picked up a female acquaintance.
The two later picked up Thomas, Harsh said, and apparently drove to Hopps Landing off of Broadfording Road several miles west of Hagerstown, where Fetterhoff was struck in the head with a rock and pushed down the embankment.
Harsh said Fetterhoff had wounds on the forehead, although he added that he did know whether the injuries resulted from the assault or the fall.
"We may never know that. I guess we won't know until we get a chance to talk to him," he said.
After the assault, Thomas drove Fetterhoff's car back toward Hagerstown until it ran out of gas near Salem Avenue just outside of the city, Harsh said. A passing motorist stopped and gave Thomas and the woman a ride into town, he said.
That ride turned out to be the key to the investigation, Harsh said. As sheriff's deputies Sunday searched the area around Fetterhoff's abandoned 1991 Ford Tempo - which had blood inside - the motorist stopped to ask what was going on.
The motorist remembered giving the pair a ride and described them to a sketch artist on Monday, Harsh said. Two other witnesses gave descriptions as well.
After hearing the description, Wayne Ditlow, a member of the Washington County Narcotics Task Force, remembered Thomas as a man arrested last Thursday - the day after Fetterhoff was reported missing.
"We just pretty much pulled the picture from the jail and Investigator Harsh took it from there," said Cpl. Robert Leatherman Jr. of the task force.
Leatherman said officials are still trying to verify Thomas' identity. When he was arrested last Thursday, he had no identification, Leatherman said.
Harsh said the woman has not been charged because she has cooperated with authorities. He said he does not know why Fetterhoff picked up the woman and Thomas, but he said there's no evidence that links him to criminal activity.