The recovered bike of a missing Louisiana college student was badly damaged, police said Wednesday, as they ruled out the possible involvement of two motorists seen in CCTV footage from the night the woman went missing.

Mickey Shunick's black bicycle had a bent back rim and damaged back tire, officers told ABC News.

Lafayette Police also told KTBS-TV that the occupants of a car and a pick-up truck seen in surveillance footage that captured Shunick as she rode home in the early hours of May 19 had been cleared of involvement in her disappearance.

The bike was discovered in a muddy basin of the Atchafalaya River on Sunday morning, nearly 30 miles from where Shunick, 22, was last seen riding home from a friend's house.

Police indicated they do not believe Shunick, a University of Louisiana anthropology major, rode her bike to the area where it was found.

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"We strongly believe that the person, or perpetrator, drove down to the edge of the water and dumped the bike into the water for it not to be found," said Paul Mouton, of the Lafayette Police Department.

Friends and family have posted fliers around Lafayette seeking information on Shunick's whereabouts. A $20,000 reward is on offer for information that helps locate her.

Police said they were still seeking the driver of a third car spotted on the surveillance footage.

Shunick is described as being 5ft 1in tall and weighing 115 pounds. She has wavy, blonde hair and was last seen wearing a pastel multicolor striped shirt, light wash denim skinny jeans, and silver ankle boots.