From the way the story seems to go, Larsen's original intent was never to shoot Tallman. Larsen approached Tallman, In regards to Tallmans unauthorized presence (Tallman's presences on the property is the original problem, not Larsen confronting a stranger on his property.) after two displays of physical violence, Larsen stated he was going to call the police, after which Tallman further assaulted Larsen, knocking the phone from his hand and the glasses from his face. 

Larsen, did not approach Tallman as a would-be vigilante lawman, but as a citizen expressing concern over Tallman alarming behavior on Larsen's property.  Only after Larsen was assaulted three times did he pull his firearm in self-defense, gave appropriate verbal warning,  and then fired.