Police said they know who the man is, and that they have interviewed him. While not calling him a suspect, police said the man has become "a significant focus" of the investigation.
The video was shot by a jewelry store security camera at 2:34 a.m. Saturday as Gardner-Quinn walked from the downtown area on Main Street of Burlington, Vt., police said. The man accompanying her is described as a white male in his mid-30s, between 5-foot-9-inches and 5-foot-11-inches tall, wearing dark blue jeans and a dark gray fleece.
Police said they again searched a house in Richmond, Vt., not far from downtown Burlington, and told FOX News that the home is linked to the man in the video, but would not elaborate. Police also wouldn't say whether the searches had turned up anything significant in the case. More searches were carried out Thursday, police said.
Gardner-Quinn, 21, of Arlington, Va., was last seen around 2:30 a.m. Saturday, Oct. 7, walking back to campus on Main Street after a night out at downtown bars with friends. Police said she was walking with a man whose cell phone she had borrowed. That man is believed to be the one in the video, police said.
Gardner-Quinn was reported missing Saturday night when she didn't show up for a planned dinner with her parents, who were visiting.
Police said it is likely the woman was abducted, but her family held out hope.
"We still have optimism that she is alive," Yasmine Rassam, Gardner-Quinn's sister, told FOX News.
Police on Thursday requested information from anyone who may have seen them together.
"While we are not naming that person or indicating that he is a suspect specifically at this time ... anyone who saw them together in that vicinity or elsewhere is asked to contact Burlington Police immediately," Deputy Chief Michael Schirling said Thursday.
Police also said they were satisfied that a man who reportedly tried to lure a woman into his white "Subaru-style" hatchback about the same time Gardner-Quinn was last seen was not a suspect.
Thursday's search spanned east of the city in Jericho and Richmond.
University of Vermont volunteers scanned the college hill section Wednesday where she was last seen looking for her gray peacoat, cardigan sweater and black purse she had been wearing.
Police have executed more search warrants but would not disclose the location of those searches.
FOX News correspondent Rick Leventhal and the Associated Press contributed to this report.