The authorities in Montana were still searching Saturday morning for an Army veteran they say opened fire inside a neighborhood bar a day earlier, killing four in what an official described as a senseless act of violence.

The suspect, Michael P. Brown, 45, fled into the rural foothills after the attack at the Owl Bar in the small town of Anaconda on Friday morning, officials said. They were searching an area west of the town after finding an abandoned white pickup truck nearby that they said he was driving.

Residents and business owners in Anaconda, a former copper smelting town near Butte in Deer Lodge County, were told to keep their doors closed and look out for the suspect.

Relatives of Mr. Brown said he had long been suffering from mental illness, including diagnosed schizophrenia.

Lee Johnson, who leads the state’s Division of Criminal Investigation, said on Friday that all four victims had been identified, but he did not name them.

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

The killings occurred on Friday morning at about 10:30 a.m. local time. Witnesses said they heard gunshots in the bar. Mr. Brown was well known around Anaconda, and social media posts show he had been to the establishment before.

Records show that he lived two houses down from the Owl Bar, a local dive with a pool table, a clutter of decorations and a sign out front that boasts the “best tap beer in town.”

Mr. Brown joined the Army in January 2001 and served in Iraq between 2004 and 2005 before leaving the service in May 2005 as a sergeant, an Army spokeswoman said. He was in the Montana National Guard for about two years until March 2008.

Two relatives of Mr. Brown said he had returned from the Army with physical ailments and severe post-traumatic stress disorder that gave him night terrors. They also said he was later diagnosed with bipolar disorder in addition to schizophrenia.

One of the relatives, a sister who spoke on the condition that her name not be used, said she and other family members had tried to get help for Mr. Brown from the Department of Veterans Affairs but that little could be done without his cooperation.

Local, state and federal agents were continuing their pursuit on foot, in vehicles and by helicopter in a region known for its brushy terrain that made the search more difficult.

“The guy could be 20 feet from us and we wouldn’t know,” said Dan Sletton, who lives near Stumptown Road west of the town, where the suspect was last seen.

Aishvarya Kavi and Kylie Mohr contributed reporting. Kirsten Noyes, Alain Delaquérière and Susan C. Beachy contributed research.