"He's innocent until proven guilty and until a court of law proves he's guilty we're again going to concentrate on trying to find her," said Dru Sjodin's brother Sven, referring to suspect Alfonso Rodriguez Jr.
An extradition hearing and arraignment for Rodriguez was to be held Wednesday morning.
"We are very confident that there's probable cause that supports his arrest yesterday and his arraignment today, and we look forward to talking with him further as this case moves forward," Grand Forks police chief John Packett said Wednesday on CBS News' The Early Show.
Investigators place Rodriguez at the mall parking lot when Sjodin was believed to be abducted, reports Bridgette Bornstein of CBS station WCCO-TV.
Searchers were asked to report Wednesday in Grand Forks and in Crookston, Minn., about 30 miles away, to help look for 22-year-old Sjodin, the University of North Dakota student from Pequot Lakes, Minn., who has been missing since Nov. 22.
The search will begin with all-terrain vehicles, with a foot search planned for later.
Packett said the arrest didn't mean the investigation was over, saying it had "only reached the 50-yard line."
"We are gaining tremendous strength and energy from the family," he told Early Show co-anchor Harry Smith. "They've been a model family to work with. They give us our energy each day and I think that is somewhat supporting the community."
He expected 1,500 volunteers for Wednesday's search, which will begin in Crookston.
Rodriguez, 50, a convicted rapist who had been released from prison in May, was arrested Monday.
Bornstein reports questions are being raised about why this man, a Level Three sex offender, was released from prison.
"He was then 50 years of age and most of the data shows that recidivism is less likely the older the offender gets," said Minnesota Corrections Commission Joan Fabian.
Authorities wouldn't say how they connected Rodriguez to the case, though they said it is routine to look at sex offenders in the area when investigating such crimes.
Rodriguez has a history of sexual contact and attempted kidnapping with adult women, and has used a weapon in at least one assault, according to a Minnesota Department of Corrections summary of his criminal history posted on the agency's Web site. His past offenses require that Rodriguez be registered as a predatory offender.
Neighbors said Rodriguez lived with his mother, Dolores. No one answered the door at their home Tuesday.
Rodriguez was released from a Minnesota prison in May after serving 23 years for an attempted abduction in Crookston in 1979. Wayne Swanson, who prosecuted Rodriguez in that case as the Polk County attorney, said Rodriguez tried to abduct a woman off the street, and stabbed her when she fought back. The woman got away, and Rodriguez was later arrested, he said.
Authorities said Sjodin may have been abducted while talking to her boyfriend, Chris Lang, on a cell phone the afternoon of Nov. 22. He called her roommate, saying he heard Sjodin say something like, "Oh, my God," before the phone went dead. During a second call a few hours later, there was only the sound of static and numbers being pressed, he said.
"Our entire focus on this is in finding Dru," Grand Forks County State's Attorney Peter Welte said. "This is by no means the end. This is a marathon and not a sprint."