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A team with the Montana National Guard has flown nearly 20 hours since last Friday, looking for any clues for Brown's whereabouts as an undisclosed number of officers searched on foot.

"Rest assured, our brave men and women of law enforcement aren’t giving up, and I ask that you not give up on them either,� Gianforte said.

Authorities say Brown, 45, fatally shot four people last Friday at The Owl Bar in the small town of Anaconda with a rifle that police believe was his personal weapon. He fled in a white pickup that he later ditched and stole another white vehicle stocked with clothes, shoes and camping supplies.

A female bartender and three male patrons were killed. They have been identified as Nancy Lauretta Kelley, 64; Daniel Edwin Baillie, 59; David Allen Leach, 70; and Tony Wayne Palm, 74.

The shooting rattled the tight-knit town of about 9,000 people, and many residents remain on high alert with the suspect still at large.

Montana Attorney General Austin Knudsen reiterated Tuesday that authorities are operating under the assumption that Brown is armed and extremely dangerous.

Without providing more details, Knudsen said there's evidence that authorities are searching in the right area. About 22 square miles (57 square kilometers) of forest southwest of Anaconda have been closed to the public by the National Forest System as the search continues. Knudsen added that it does not appear that Brown has broken into any cabins or homes in the area to get food or additional supplies.

Knudsen and investigators declined to share the number of law enforcement personnel active in the search Tuesday. Canine detection units and drones equipped with heat-detection technology were also being used in the search, they said.

Federal authorities were offering a reward of up to $10,000 for any information leading to Brown’s capture.

Family members have said Brown has struggled with mental illness for years, and they had sought help for him.

Brown, who lived next door to The Owl Bar, served in the Army as an armor crewman from 2001 to 2005 and deployed to Iraq from early 2004 until March 2005. He also was in the Montana National Guard from 2006 to 2009.