ANACONDA, Mont. — Authorities are scouring a mountainous area of western Montana for a military veteran who they say opened fire at a bar, killing four people.

Michael Paul Brown, 45, fled The Owl Bar in the small town of Anaconda in a white pickup truck but ditched it at some point, said Lee Johnson, administrator of the Montana Division of Criminal Investigation, which is overseeing the case. He urged residents late Friday to stay at home and on high alert.

“While law enforcement has not received reports of Brown harming any other individuals, he is believed to be armed, and he is extremely dangerous,” Johnson said.

Authorities said they would release the names of the victims once all of their families have been notified.

“This is a small tight-knit community that has been harmed by the heinous actions of one individual who does not represent what this community or Montanans stand for,” Johnson said.

Anaconda, about 25 miles (40 kilometers) northwest of Butte, is hemmed in by mountains. The town of about 9,000 people, was founded by copper barons who profited off nearby mines in the late 1800s. A smelter stack that’s no longer operational looms over the valley.

Brown lived next door to The Owl Bar, said owner David Gwerder, who wasn’t there during the shooting Friday morning. Gwerder told The Associated Press that the bartender and three patrons were killed and didn’t think anyone else was inside. He also said he wasn’t aware of any conflicts between Brown and any of the victims.

“He knew everybody that was in that bar. I guarantee you that,” Gwerder said. “He didn’t have any running dispute with any of them. I just think he snapped.”

Brown served in the U.S. Army as an armor crewman from 2001 to 2005 and deployed to Iraq from early 2004 until March 2005, said Lt. Col. Ruth Castro, an Army spokesperson. Brown was in the Montana National Guard from 2006 to March 2009, Castro said. He left military service in the rank of sergeant.

Brown’s niece, Clare Boyle, told the AP on Friday that her uncle has struggled with mental illness for years and that she and her other family members repeatedly sought help.

“This isn’t just a drunk/high man going wild,” she wrote in a Facebook message. “It’s a sick man who doesn’t know who he is sometimes and frequently doesn’t know where or when he is either.”

With no sign of Brown in the white pickup or his home, authorities converged on the Stumptown Road area west of Anaconda by ground and air, locking it down so no one was allowed in or out. A helicopter hovered over a nearby mountainside as officers moved among the trees, said Randy Clark, a retired police officer who lives there.

As reports of the shooting spread through town earlier Friday, business owners locked their doors and sheltered inside with customers.

The owner of the Firefly Café in Anaconda said she locked up her business after a friend alerted her to the shooting.

“We are Montana, so guns are not new to us,” Barbie Nelson said. “For our town to be locked down, everybody’s pretty rattled.”