Wrapped in insulated gear and traveling in Humvees, the troops were targeting isolated areas.
Investigators found about a three-hour gap between the time a North Dakota college student disappeared and the time the suspect in the case arrived home, according to a search warrant unsealed Thursday.
Alfonso Rodriguez Jr. was at the Crookston, Minn., home he shares with his mother about 8:15 p.m. on Nov. 22, Dolores Rodriguez told police, according to the Dec. 2 search warrant.
Sjodin, a 22-year-old student at the University of North Dakota, was last seen that day in Grand Forks, about 25 miles west of Crookston. About 5 p.m., she had spoken to her boyfriend via cell phone from the parking lot of the mall where she worked.
Her boyfriend, Chris Lang, admits he wasn't concerned at first; it just sounded like ordinary cell phone drop-out.
"The urgency of it was not there at the time," he said Friday on CBS News' The Early Show.
An affidavit unsealed Tuesday showed Rodriguez told authorities he had watched a movie, "Once Upon a Time in Mexico," at the mall during that time, but authorities said that movie was not playing at the mall or anywhere nearby that day.
When confronted, Rodriguez "did not have an explanation" for the fact that the movie he named wasn't showing, according to the officer who applied for the search warrant. Its contents were first reported by The Forum of Fargo.
The search warrant showed Rodriguez cooperated with an initial search of his car Nov. 26, but refused a second search and asked for a lawyer. Police raided his house nine hours later.
Among the items seized were receipts from stores near the Columbia Mall time-stamped Nov. 22, swabs of "apparent blood" from the garage floor and three latex gloves from his car trunk, the papers unsealed Thursday show.
Rodriguez, 50, has said he is innocent. Charged with kidnapping, he is jailed in Grand Forks on $5 million bond.
The National Guard takes over as the recent bitterly cold weather has made search conditions too dangerous for civilian volunteers. Lang said the support of the community has been wonderful.
"There's been an incredible effort to find her. We just need to keep that going and keep that strong, but it's been incredible, the people in this town, people in the country," he told Early Show co-anchor Rene Syler. "She's in everybody's consciousness, as well she should be, because she's wonderful and we'll just keep looking."