The suspect, identified by authorities as 45-year-old Michael Paul Brown of Anaconda, fled the scene and is believed to be "armed and dangerous," Lee Johnson, with the Montana Department of Justice, told reporters at a brief news conference Friday night.
Police located the 2007 white Ford F-150 pickup Brown was last seen driving earlier Friday but he was not in it, and authorities are now concentrating their search along Stumptown Road, a highway west of Anaconda, Johnson said.
"Residents of the area have been notified and are encouraged to stay inside their homes and on high alert," Johnson said.
Authorities haven't said what led up to the shooting at the bar or a possible motive.
Police have identified the four people killed but are not yet releasing their names until they've had a chance to talk to family members, Johnson said.
The shooting sparked a large law enforcement presence, including the Bureau of Alcohol, Tobacco, Firearms and Explosives, which sent agents to respond to the scene.
Earlier in the day, Montana Gov. Greg Gianforte said on social media that he was "closely monitoring the situation involving an active shooter in Anaconda" and asked for prayers for the victims.
