Her body had been in the field for more than a week about 8 miles from the house where she last was seen early Jan. 20 at the edge of the University of Nevada, Reno, he said.
"I would say this is a serial rapist," Johns said at a news conference. "We have two, probably three (cases) linked through DNA."
"The totality of the information in this case leads us to believe it is a sexually motivated crime," he said. "I'm worried this guy is still out there, and I'm worried somebody else is going to get hurt."
Campus officers will do all they can to support investigators "in hunting this animal down and bringing him to justice," said university Police Chief Adam Garcia.
Heavy snowfall over the past few weeks may have delayed the discovery of her body, police said.
Denison was abducted by a suspected rapist that police have linked by DNA to a string of attacks near the Reno campus. A student at Santa Barbara City College in California, she was visiting her hometown over winter break and was last seen sleeping on a couch at a friend's rental house just off campus.
DNA evidence links Denison's kidnapping to two other attacks on women near the university late last year, police said, and an earlier campus attack also could be related.
In that earlier incident, the attacker brazenly raped a woman at gunpoint in a parking garage where campus police park their cruisers.
Based on partial descriptions from previous victims, police have described the suspect as a white male between ages 28 and 40 and at least 5 feet 6, with a long face and brown hair. He was believed to have no accent or regional dialect.
he killer's familiarity with the city suggests he likely lives in Reno, Johns said, adding that he believes the "chances are very good" they will catch him.
"It could be tomorrow, next month, next year. We are going to find this suspect," he told reporters.
The killer probably lives near the campus just north of the downtown casino district or on the city's nearby northwest side, Johns said, and he may work closer to the city's southeast side, where the body was found.
"Somewhere in our community there is a wife, a mom, a girlfriend, a sister who recognizes this suspect. Likely he looks like somebody you would least suspect, but that is the person who is responsible for this crime," he said.
Publicity of the manhunt may cause the rapist to stop attacking, but "our absolute fear is he may re-offend," Johns said.
Denison's disappearance generated an outpouring of support from the community. Hundreds of volunteers aided in daily searches in and around Reno, and electronic casino marquees featured her photograph.
One of the "Bring Bri Back" fliers with her photo and information about a suspect and suspect vehicle was tacked to a telephone pole on the corner of the field where her body was found about noon on Friday.
Bridgette Denison, Brianna's mother, issued a statement on behalf of the family Saturday thanking police and the community for their help in the search for her daughter.
"On March 29, 1988, Bridgette and Jeffrey Denison were given the incredible gift of their daughter Brianna. On January 20, 2008, she became the daughter of our entire community," she said in the statement.
Bridgette Denison asked that every woman in the community "be diligent about their own safety."
"We ask once again that if there is anyone out there with information, we beg you to come forward."
