Authorities were scouring a mountainous area of western Montana for a military veteran who they say opened fire at a bar in the small town of Anaconda, killing four people.

ABC News contributor and former NYPD chief Robert Boyce breaks down the ongoing police investigation after a gunman opened fire at a Montana bar, killing at least four people.

Former FBI TEDAC Director Scott Sweetow discusses the search for suspect Michael Paul Brown, who is accused of shooting and killing four at a bar in Anaconda, Montana.