The preliminary DNA match would be the most significant break yet in the attempt by authorities to tie convicted rapist Alfonso Rodriguez Jr. to Sjodin's disappearance. Hill said investigators tested blood from Rodriguez's car against DNA taken from Sjodin's toothbrush. Hill described the blood in the car as a small amount.
CBS News Early Show National Correspondent Jon Frankel reports blood found on a knife discovered in the car's trunk also matches Sjodin's.
"I certainly hate to be discouraging to the family or anyone, but it looks to me now that it's more of a recovery mission than a rescue," Grand Forks County Sheriff Dan Hill said.
In an interview with The Associated Press, Hill also revealed that searchers found a shoe belonging to the University of North Dakota student near the Red Lake River after she disappeared. Sjodin was last heard from Nov. 22, calling her boyfriend on a cell phone from the parking lot of a Grand Forks mall where she worked at a Victoria's Secret.
A college roommate of Sjodin, 22, identified the shoe. It is the only piece of clothing recovered so far, Hill said.
It's also been reported that a knife sheath was found near Sjodin's car in the parking lot of the Grand Forks shopping mall where she disappeared. That sheath could only belong to a particular knife sold exclusively as a set in a home improvement store in Grand Forks, a source told the Star Tribune of Minneapolis.
Hill also confirmed a media report that the interior of Rodriguez's car and its trunk had been extensively cleaned before his arrest.
Rodriguez, 50, has been charged with Sjodin's kidnapping. He has said through his attorney that he is innocent.
Sjodin's father said Monday he was dismayed to find that police recovered a knife from Rodriguez's car. But given his criminal past, he said he was not surprised.
"You know what? It's probably true," Allan Sjodin said. "That's his modus operandi."
Documents in the case were expected to be made public later Tuesday.
Rodriguez has a history of attempted kidnapping with adult women, and has used a weapon in at least one assault. Rodriguez was released from a Minnesota prison in May after serving 23 years for an attempted abduction in 1979.