By Karina Tsui, Michelle Watson, Holly Yan, CNN

(CNN) — The manhunt for an Army veteran suspected of killing four people at a bar he frequented has expanded in the rugged Montana terrain, authorities said.

Michael Paul Brown is still on the run Monday, three days after authorities said he opened fire at The Owl Bar in Anaconda, on the western side of Montana.

Brown is believed to be armed and dangerous, Montana Attorney General Austin Knudsen said. Officials are offering a $7,500 reward for information leading to his capture.

Local, state and federal authorities have been scouring the wilderness by land and air. But it’s still unclear why Brown allegedly killed four people at the bar around 10:30 a.m. Friday before fleeing in his underwear.

Victims include a beloved retired nurse

The

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