The May 31 incident came to light when the victim showed up at Washington County Hospital and Hagerstown City Police were called.
She told police she was with friends during the evening of May 30 and ended the night at a friend's home on Jonathan Street.
She told police she left at 5 a.m. and began walking on Church Street in Hagerstown when a car pulled up behind her and the driver yelled something out the window.
When the woman walked up to the car, the driver produced a knife and ordered her into the car, police reports said.
Somewhere off Broadfording Road, the man pulled over and ordered the victim to perform oral sex, police reports said.
All the while, the man was holding the knife, the victim told police.
She said she did what he wanted her to do briefly but struggled to get away, causing her blouse to be ripped.
Police said the victim's blouse was ripped when they saw her at the emergency room.
The investigation began with interviews with several friends of the victim who said they recognized the description of the man and his car.
On June 3, the woman picked Gardner's likeness out of a photo line-up, according to police.
When approached on June 20, he first denied the allegations but later admitted picking the woman up, driving into the country and asking her to perform oral sex , police reports said.
He denied having a weapon or using any force on her, according to police.