State Police Cpl. George Stottlemyer, of the Frederick barracks, said the man held the woman overnight and then ordered her back on the road the next morning. At some point, the woman stopped the car and the man got out, he said.
"He just gets out, closes the door and she leaves," Stottlemyer said.
State police in Chambersburg, Pa., and Frederick launched a joint investigation.
Stottlemyer said the woman tried to show Pennsylvania authorities where the rape occurred but could not find the spot.
"She has not been able to recall the exact location," he said.
The woman was examined at Washington County Hospital, said Sgt. Kevin Gardner of the Frederick barracks.
Even though the abduction occurred in Hagerstown, Stottlemyer said the Frederick barracks is investigating because the case began as a missing person's report.
When the woman did not return home Monday night, her husband reported her missing to Frederick authorities, Stottlemyer said. Investigators were talking with her husband at their home when she returned Tuesday morning, police said.
Since Frederick investigators had a head start, Stottlemyer said police in Hagerstown agreed it made more sense for them to continue with the investigation.
Hagerstown Police Chief Dale J. Jones said switching investigators in midstream does not make sense.
"It happens occasionally, depending on the circumstances," he said. "They've already completed a considerable part of the initial investigation. It makes sense for them to continue, rather than involving a third police agency."
Employees at businesses near the intersection where the woman said the abduction occurred expressed shock that a motorist could be kidnapped at gunpoint on a busy road in broad daylight.
"Isn't that something," said Charlie Blubaugh, manager of Duncan Bros. Tire Co., on Dual Highway near Manor Drive.
Blubaugh said he was amazed he hadn't heard anything about the incident before, especially since the busy intersection can be easily seen from the waiting room window of his business.
A manager at the Dual Highway Dairy Queen, who was on duty Monday afternoon, said she also had heard nothing about the incident, not even a rumor among customers and employees.
The manager, who asked not to be identified, said it concerns her that police did not release any information about the incident sooner. "Because I'm scared," she said.
"You need to be aware, even if you are just being cautious," she added.
Jones said his department was not notified about the incident until Wednesday. He said the department did not notify local media because it is not involved in the investigation.
Police Thursday said the gunman was described as a white man with a dark, ruddy complexion. He is about 25 years old, is about 6 feet tall and has reddish hair. On the day of the abduction, he was wearing a dark navy shirt and trousers, black, shiny boots and a dark jacket.
Staff Writer Guy Fletcher contributed to this story.